• Share
  • Email
  • Embed
  • Like
  • Private Content
VNX Snapshots
 

VNX Snapshots

on

  • 6,005 views

This white paper describes EMC VNX Snapshots. The paper reviews and explains operations and best practices for the feature, as well as limits and functions.

This white paper describes EMC VNX Snapshots. The paper reviews and explains operations and best practices for the feature, as well as limits and functions.

Statistics

Views

Total Views
6,005
Views on SlideShare
6,005
Embed Views
0

Actions

Likes
1
Downloads
157
Comments
0

0 Embeds 0

No embeds

Accessibility

Categories

Upload Details

Uploaded via as Adobe PDF

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

    VNX Snapshots VNX Snapshots Document Transcript

    • White PaperVNX Snapshots Abstract This white paper describes EMC VNX Snapshots. The paper reviews and explains operations and best practices for the feature, as well as limits and functions. July 2012 VNX Snapshots White Paper 1
    • Copyright © 2012 EMC Corporation. All RightsReserved.EMC believes the information in this publication isaccurate as of its publication date. The informationis subject to change without notice.The information in this publication is provided “asis.” EMC Corporation makes no representations orwarranties of any kind with respect to theinformation in this publication, and specificallydisclaims implied warranties of merchantability orfitness for a particular purpose.Use, copying, and distribution of any EMC softwaredescribed in this publication requires anapplicable software license.For the most up-to-date listing of EMC productnames, see EMC Corporation Trademarks onEMC.com.Part Number H10858 VNX Snapshots White Paper 2
    • Table of ContentsExecutive summary ........................................................................................... 5Audience ......................................................................................................... 5VNX Snapshots Technical Overview ..................................................................... 6 What is new? .................................................................................................................... 6 How do Snapshots work? ................................................................................................ 6 Snapshot granularity ................................................................................................... 8 Snapshot Mount Point..................................................................................................... 9VNX operations............................................................................................... 11 Create a Snap .................................................................................................................11 Create a Snapshot Mount Point....................................................................................13 Attach a Snap .................................................................................................................14 Branching (snap of a snap) ...........................................................................................15 Copy a Snapshot........................................................................................................15 Snap of a Snapshot Mount Point .............................................................................17 Detach a Snapshot Mount Point...............................................................................19 Detach a Snapshot Mount Point with Snapshots ...................................................20 Destroy a Snapshot .......................................................................................................22 Consistency Groups.......................................................................................................23 Attach a Consistent Snapshot ..................................................................................24 Branch a Consistent Snapshot .................................................................................27 Rules for Consistency Groups ...................................................................................28 Restore............................................................................................................................28 Restore with SnapView Snapshots and VNX Snapshots ........................................29 Restore a LUN.............................................................................................................29 Restore CGs ................................................................................................................31 Repurpose Snapshots ...................................................................................................31 Migrations ......................................................................................................................32 Migration considerations ..........................................................................................35 Limits ..............................................................................................................................35VNX Snapshot Auto-Delete ............................................................................... 36 Auto-Delete Thresholds .................................................................................................37 Pool Space Used Threshold ..........................................................................................37 Snapshot Space Used Threshold .............................................................................38 Delete Eligibility .............................................................................................................39 Auto-Delete paused .......................................................................................................39 VNX Snapshots White Paper 3
    • Snapshot Expiration ......................................................................................................40CLI ................................................................................................................ 41 Create a Snapshot .........................................................................................................41 Copy a Snapshot ............................................................................................................42 Create a Snapshot Mount Point....................................................................................42 Attach a Snapshot .........................................................................................................43 Create a Cascading Snapshot .......................................................................................43 Detach a Snapshot ........................................................................................................44 Destroy a Snapshot .......................................................................................................44 List all VNX Snapshots for a LUN ..................................................................................44 Create a Consistency Group ..........................................................................................45 List Consistency Groups ................................................................................................45 Create a Consistent Snapshot ......................................................................................46 Attach a Consistent Snapshot ......................................................................................46SnapCLI ......................................................................................................... 47 Flush buffers ..................................................................................................................47 Create a Snapshot .........................................................................................................47 Attach a Snapshot .........................................................................................................47 Copy a Snap ...................................................................................................................47 Consistency Groups.......................................................................................................48 Sample SnapCLI batch script ........................................................................................48VNX Snapshots vs. SnapView terms .................................................................. 49Terminology ................................................................................................... 50Properties Detailed ......................................................................................... 51 Snapshot properties ......................................................................................................51 Snapshot Mount Point properties ................................................................................52 Additional pool properties ............................................................................................53 VNX Snapshots White Paper 4
    • Executive summaryVNX™ Snapshots is a new VNX software feature that creates point-in-time data copies. VNX Snapshots is used for data backups, softwaredevelopment and testing, repurposing, data validation, and local rapidrestores. Unlike SnapView™ snapshots and clones, VNX snapshots donot consume large amounts of pool capacity. As a result, this feature ispreferred for modern data management.This white paper describes all VNX Snapshots operations in detail.Wherever possible, all aspects of the feature sets are presented visually.The paper provides straightforward instructions for common functionaltasks. Most tasks are shown from the point of view of Unisphere™(graphical user interface) and naviseccli (command line interface).VNX Snapshots and SnapView will coexist on the same LUN.Furthermore, SnapView clones, which use a different technology fromSnapView snapshots, will work with VNX Snapshots.AudienceThis paper is intended for EMC customers and EMC field personnel whoare familiar with VNX technology. The paper is intended to be used as amain reference for VNX Snapshot technology. VNX Snapshots White Paper 5
    • VNX Snapshots Technical OverviewWhat is new?VNX Snapshots is a new feature introduced in VNX for Block OE Release32. It was created to improve on the existing SnapView Snapshotfunctionality by better integrating with pools. In fact, VNX Snapshots canonly be used with pool LUNs.LUNs that are created on physical RAID groups, also called RAID LUNs,support only SnapView Snapshots. This limitation exists because VNXSnapshots require pool space as part of the technology.Note: SnapView Snapshots are compatible with pool LUNs. VNXSnapshots and SnapView Snapshots can coexist on the same pool LUN.VNX Snapshots support 256 writeable snaps per pool LUN. It supportsBranching, also called Snap of a Snap. There are no restrictions to thenumber of branches, as long as the total number of snapshots for agiven primary LUN is within 256, which is the hard limit.Consistency Groups are also introduced in this release. Several poolLUNs can be combined into a Consistency Group and snappedconcurrently.How do Snapshots work?VNX Snapshots use redirect on write (ROW) technology. ROW redirectsnew writes destined for the primary LUN to a new location in the storagepool. Such an implementation is different from copy on first write(COFW) used in SnapView, where the writes to the primary LUN are helduntil the original data is copied to the reserved LUN pool to preserve asnapshot.Figure 1 compares the two technologies. VNX Snapshots White Paper 6
    • Figure 1: SnapView write vs. VNX Snapshot writeIn Figure 1, the main difference between SnapView Snapshot and VNXSnapshot is evident. VNX Snapshot technology writes the new data to anew area within a pool, without the need to read/write to the old datablock. This improves the overall performance compared to SnapView.Similarly, during a read from a snapshot, the snapshots data does notneed to be constructed from two different places as shown in Figure 4Figure 2: SnapView read vs. VNX Snapshot read VNX Snapshots White Paper 7
    • Snapshot granularityEvery VNX Snapshot has 8 KiB block granularity. This means that everywrite occupies at least 8 KiB on the pool. The distribution of the 8 KiBblocks within a 1 GiB slice is congruent with the normal thin writealgorithm.Consider the following example. A LUN is snapped with a few blocks ofdata. The new snapshot points at those blocks, just like the primaryLUN. Figure 3: VNX Snapshot pointing at the same blocks with the LUN at creation timeAfter a few moments, the primary LUN may receive an I/O that overwritesblock A. The first snapshot continues pointing to the original set ofblocks A, B, C, and D. After Snap2 is taken, it points to A`, B, C and D.The next primary LUN I/O overwrites block D, and it now points to A`, B,C, and D`.Figure 4: VNX Snapshots point at unchanged blocks, Primary LUN is using new blocks VNX Snapshots White Paper 8
    • Thick LUN considerationWhen a VNX Snapshot is created on a Thick LUN, portions of its addressspace are changed to indirect mode. In other words, when writes comein to the Snapped Thick LUN, the LUN starts converting address mappingfrom direct to 8KiB blocks for each portion of the Thick LUN beingwritten.Note: Thick LUN remains to be classified as Thick in the CLI and GUI.The Thick LUN remains in an indirect mode while it has VNX Snapshots.When the last snapshot of the Thick LUN is removed, the modeautomatically converts to direct . The conversion to direct mode is notinstantaneous, and is performed in the background. The conversion canbe aborted by creating a new VNX Snapshot on the LUN.VNX Snapshots are a part of the storage pool. A snapshot does notconsume space from the pool, until the new data is written to theprimary LUN or to the snapshot itself.Snapshot Mount PointSnapshot Mount Point (SMP) is a virtual LUN-like container. It is used toemulate a typical LUN, but provides the ability for the host to write tosnapshots and to change snapshots without the need to rescan the SCSIbus on the client.Figure 5: What is a Snapshot Mount Point? VNX Snapshots White Paper 9
    • An SMP is created for snapshots of a specific LUN. This means that eachSMP can be used only for snapshots of a single primary LUN.To enable access to hosts, SMPs must be provisioned to storage groupsjust like any typical LUN. VNX Snapshots White Paper 10
    • VNX operationsVNX Snapshots support the following operations.Create a SnapCreating a snapshot does not consume any pool space. The space startsbeing used when new writes to the primary LUN or the snapshot itseldarrive. Snapshots have a granularity of 8 KiB, and thier blocks aretracked just like the blocks in thin LUNs.Figure 6: A pair of VNX SnapshotsEvery snapshot must have a primary LUN, and that property neverchanges. A primary LUN cannot be deleted while it has snapshots. InUnisphere, you can delete a LUN that has snapshots by selecting anoptional setting that deletes the snapshots first.To create a snapshot:1. In Unisphere, select Storage > LUNs.Figure 7: Create VNX Snapshots in Unisphere VNX Snapshots White Paper 11
    • 2. Click Create Snapshot or right-click the primary LUN.# To create snapshot in the CLInaviseccli snap -create -res 1 -name "cli_snap" -descr "snap created via CLI" # ^^^ # LUN IDWhen a snapshot is first created, it is write-protected:Figure 8: Unisphere view of the VNX Snapshot write protectionWhen you try to attach a snapshot that has the Allow Read/Write optiondisabled, Unisphere automatically enables it and displays a warning.Figure 9: Unisphere VNX Snapshot Attach warningIf a Snapshot is attached from the CLI, then the -allowReadWrite propertymust be set to Yes. Therefore, you must manually modify it prior to anattach command. VNX Snapshots White Paper 12
    • Before creating a snapshot, use the SnapCLI utility to flush the hostbuffers.:: WindowsSnapCLI flush -o G:# To modify a snap in the CLInaviseccli snap -modify -id "cli_snap" -allowReadWrite yesCreate a Snapshot Mount PointTo create an SMP in Unisphere, use the Configure Snapshot Mount Pointwizard located in Data Protection > Common Data Protection Tasks. Thewizard is also available in the Wizards area on the right pane.Figure 10: Unisphere Snapshot Mount Point creation wizard locationAlternatively, you can also create an SMP by right clicking on a LUNlisted in the LUN tab under Storage > LUNs.Figure 11: Unisphere right mouse click Snapshot Mount Point creationCreating an SMP does not require any space from the pool. VNX Snapshots White Paper 13
    • Note: Each SMP is dedicated to a specific primary LUN. It is not possibleto attach snapshots from two different primary LUNs to a single SMP.Therefore, a backup server that is backing up four different LUNs musthave four different SMPs provisioned to back up the snapshots of thoseLUNs.In Unisphere, you can provision the SMP to a host through either thewizard or the SMP create screen.In the CLI, you can provision the SMP to a host by using the StorageGroup command:# To create a Snapshot Mount Point in CLInaviseccli lun -create -type Snap -primaryLunName PrimaryLUN -sp B -l 60 -name SMP_name -allowInbandSnapAttach yes # ^^ SMP LUN ID!!!# When LUN ID is not provided at creation, VNX assigns one automatically.# in that case, it needs to be looked up in order# to provision the SMP to a storage group# To provision the SMP to a Storage Groupnaviseccli storagegroup -addhlu -gname "Storage Group 1" -hlu 60 -alu 60CLI guidelines • Create the SMP on the same Storage Processor as the primary LUN • Set the -allowInbandSnapAttach parameter to "yes" to allow SnapCLI host binary to attach the Snapshots (It is a security feature. The Troubleshooting section provides more details.) o This parameter can easily be modified at a later time. • An SMP is added to a storage group just like a usual LUN.Attach a SnapAttaching is an asynchronous operation during which the SMP remainsavailable, but the I/O is queued. This means that that the host does nothave to rescan the SCSI bus to view the snapshot. The rescan is requiredonly to discover the SMP when it is first presented to the host. VNX Snapshots White Paper 14
    • Figure 12: Attaching a Snapshot to a Snapshot Mount Point Note: A SCSI rescan is not required for switching attached snapshots, that is, detaching one snapshot and attaching another to the same SMP. However, you must stop all I/O to the SMP and most importantly, flush the host buffers (using the SnapCLI utility). Branching (snap of a snap) There are two main ways to create a Snap of a Snap. One way is to create a simple copy of a Snapshot and another is to take a Snapshot of the attached Mount Point, for example, Cascading Snapshots. Copy a Snapshot A VNX Snapshot can be copied to another snapshot. The resulting snapshot is a copy of the source except for the name. The - allowReadWrite1 property is set to No on the copy. The snapshot copy retains the source LUN properties and resides within the same pool as the original snapshot. So, copying a snapshot increases snapshot count by one.1 This property is a security feature, preventing unauthorized mounting a snapshot for read/write operations. VNX Snapshots White Paper 15
    • Figure 13: VNX Snapshot copyNote: Only unattached snapshots can be copied. Attached snapshotsare branched by snapping SMP, a process that is also called CascadingSnapshots. VNX Snapshots White Paper 16
    • Snap of a Snapshot Mount PointA snapshot of an SMP still has the same Primary LUN property as theMount Point (and as the attached snapshot. The primary LUN propertiesof snapshots and the mount points that they are attached to will neverbe different)It is technically possible to attach a snapshot to an SMP that is not apart of a storage group. Therefore, it is possible to create a snapshot ofsuch an SMP. The resulting snapshot will be slightly different from aregular snapshot copy. The source of this snapshot and the creationtimes will not be the same as the snapshot attached to the SMP.Figure 14: VNX Snap of a Snap, aka Cascading Snapshots VNX Snapshots White Paper 17
    • The Source LUN property of the Cascading Snapshot has the name of theSMP. It is possible to create multiple snapshots at this level, andindividually mount them.Figure 15: VNX Snapshots, multiple levelsNote: In Figure 14 and Figure 15, both SMPs may only be used forPrimary LUN1 Snaps. No other snapshots may be attached to them.However, either SMP could be provisioned to any host.. VNX Snapshots White Paper 18
    • Detach a Snapshot Mount PointDetaching a snapshot from an SMP modifies these properties: LastModified Date and Last Modified By. Detaching a snapshot from an SMPdoes not destroy the SMP by default, and the SMP stays provisioned tothe host. Detaching is an asynchronous operation during which the SMPremains available, but the host I/O is queued at the array. After thedetach operation completes, all queued I/O requests return a fail statusto the host.Figure 16: Detaching a VNX Snapshot VNX Snapshots White Paper 19
    • Detach a Snapshot Mount Point with SnapshotsDetaching a snapshot from an SMP is more complex when the SMP hasa few of its own snapshots.Figure 17: Detaching SMP with its own SnapshotsFigure 17 shows that as a result of Snap2 detaching from SMP1, thesecond level snapshots (Snap2.1 and Snap2.2) need to change: • The Source LUN property to match a higher-level object, which is Primary LUN1. • The Creation time to match Snap2 (original Snap attached to SMP1) • The Last modify time to match the old Last modified time or Creation time (if Last modified was empty) or remains the same, if the snapshot had not been modified (as Snap2.2 has in Figure 17). VNX Snapshots White Paper 20
    • Similarly, a multilevel structure will change as shown in Figure 18.Figure 18: Multi-level detaching SMP with its own SnapshotsNote: A detached SMP persists by default and is kept provisioned to thehost. There is no degradation in the array performance during thedetaching operation.When users are about to detach an SMP, Unisphere displays a messageasking users to stop I/O and flush the host buffers.Figure 19: Unisphere Snapshot detach confirmationEMC recommends flushing the buffers by using the SnapCLI utility onthe host. For example::: Windows. flush the buffers for drive G:SnapCLI.exe flush -o G: VNX Snapshots White Paper 21
    • Destroy a SnapshotDestroying (deleting) a snapshot reclaims space for reuse in the storagepool. Reclaim is not instant, and is done by an internal process. Thisinternal process is throttled for better performance of the array and isnot sequential, that means, more than one snapshot can be destroyedat one time. Multiple snapshot destructions start on the first-come-first-served basis. VNX is tuned to destroy up to 16 snapshotssimultaneously on each Storage Processor (SP). Additional destructionrequests are queued until a destruction thread becomes available.When a snapshot is in the "Destroying" state, it is still counted towardsthe maximum number of snapshots. The snapshot name is changed toDestroying_<timestamp> before it is destroyed. This way, a user can re-create a snapshot called "Monday_Backup_Snapshot" immediatelyafter executing a command to destroy the old snapshot . This isespecially useful for SnapCLI-based scripts.After the destruction command is accepted by the array, actualdestruction may take different amounts of time to complete. The timedifference is dependent on several factors such as the amount of datawithin a Snap, the SP CPU load, and the speed of the underlying diskswithin a pool. VNX Snapshots White Paper 22
    • Consistency GroupsA Consistency Group (CG) is an object that contains a list of primaryLUNs or SMPs (but not both) that are treated as a single entity for takingsnapshots.A Consistent Snapshot is one snapshot of a collection of LUNs. When asnapshot of a CG is initiated, all writes to member LUNs are held untiltheir snapshots have been created. Typically, CGs are used for LUNs thatbelong to the same application.Note: Application-side consistency is achieved with AppSync productthat integrates with VNX Snapshots and VNX Snapshot CGs.CGs are intended to take write-order–consistent snapshots of a group ofLUNs or SMPs. CGs have a name and description. CGs can contain anynon-private pool-based LUNs, or SMPs.Figure 20: VNX Snapshot Consistency GroupFigure 21: Unisphere view of a Consistency Group VNX Snapshots White Paper 23
    • Attach a Consistent SnapshotMounting an entire Consistent Snapshot requires the same number ofSMPs as there are members in the CG.Figure 22: Attaching a Consistent SnapshotNote: A Consistent Snapshot may have different number of snapshotsthan a CG, if the CG’s members were modified after the snapshot wastaken.It is technically possible to attach a single snapshot from the ConsistentSnapshot. The system checks the SMPs primary LUN to know whichportion of the Consistent Snapshot to attach. VNX Snapshots White Paper 24
    • Figure 23: Attaching individual SMPs to a Consistent SnapshotHowever, when SMPs are also members of a CG, they can be attached toonly one consistent snapshot. Figure 24 displays a bad example thatdoes not work.The main difference between Figure 24 and Figure 23 is that SMPs inFigure 23 are not in a CG, and SMPs in Figure 24 are. VNX Snapshots White Paper 25
    • Figure 24: SMPs that are members in a CG cannot be attached to different Consistent Snapshots VNX Snapshots White Paper 26
    • Branch a Consistent SnapshotConsistent Snapshots can be branched just like regular snapshots.Figure 25: Attaching a Copy of a Consistent Snapshot VNX Snapshots White Paper 27
    • Cascading Consistent SnapshotsTo create a cascading Consistent Snapshot, a new CG must be createdout of SMPs attached to a snapshot.Figure 26: Attaching a Cascading Consistent SnapshotRules for Consistency Groups The rules for CGs are: • CGs must not contain a combination of primary LUNs and SMPs • CGs must not contain multiple SMPs from the same primary LUN • Any LUN/SMP can belong to only one CG • SMPs that are members in a CG cannot be attached to different Consistent Snapshots • Consistent Snapshots for RAID LUNs or a mix of RAID LUNs and Thick/Thin LUNs are only possible with SnapView snapshots (sessions)RestoreSnapshots can be used to restore a primary LUN or an SMP. In otherwords, the data in the LUN will be changed to match the data in thesnapshot. The classic use case for this operation is when recoveringfrom data corruption. VNX Snapshots White Paper 28
    • Restoring automatically creates a Restore point snapshot to recoverfrom unintentional data corruption. Although restoring is not instant, itis an online operation. While the LUN is being restored, its state showsas Initializing, and is changed back to Ready after the restore iscomplete.Note: Restoring is also referred to as Protected Restore, becauserestoring does not change the snapshot. All its data is protected.When restoring an SMP, the data from the source snapshot (the onebeing restored) is placed onto the snapshot attached to a Mount Point.Note: Restoring can change the LUN size if the source snapshot wastaken before the primary LUN expansion or shrinking.Restore with SnapView Snapshots and VNX SnapshotsSince pool LUNs can have a combination of SnapView snapshots andVNX Snapshots, it is possible to restore from either a SnapViewsnapshot or a VNX Snapshot. Restore is supported for both cases. • To restore a primary LUN from a VNX Snapshot, all SnapView snapshots (sessions) must be manually deleted (stopped). • If the primary LUN is restored from a SnapView snapshot (session), VNX Snapshots are unaffected.Figure 27: Unisphere error on Snapshot restore due to the presence of a SnapView sessionRestore a LUNCertain prerequisite steps must be performed from the host operatingsystem for a successful LUN restoration. Operating Systems often havecached metadata pertaining to the LUNs file system. Restore operationstend to confuse memory maps unless the cache is cleared.This affects most operating systems. The following is a sampleprocedure to restore a LUN from a VNX Snapshot. Microsoft Windowsoperating system is used as an example.Step 1Stop application access to the LUN. Optionally, you may need to flushapplication buffers. VNX Snapshots White Paper 29
    • Step 2Flush the buffers for the drive by using SnapCLI .Note: EMC recommends using SnapCLI for all other operating systems (ifan appropriate binary exists). Use native operating system methodswhen SnapCLI binary is not available.:: WindowsSnapCLI flush -o G::: Optionally, one could flush a physical drive, when it is not a "drive letter":: Note, this command makes sense only when the drive is mounted,:: e.g. has a drive letter assignedSnapCLI flush -o .PhysicalDrive1Step 3Unmount the drive. For some versions of Windows, unmounting refers toremoving the drive letter. Windows 2008 has an option to turn the driveoffline. This can be done either from Disk Management or from the CLI(diskpart).Note: Unmounting the drive guarantees that the host stops all I/O to theLUN.Figure 28: Windows 2008 Disk Manager -- switching a disk to offline modeC:>diskpartMicrosoft DiskPart version 6.1.7601Copyright (C) 1999-2008 Microsoft Corporation.On computer: WIN2K8DISKPART> list disk VNX Snapshots White Paper 30
    • Disk ### Status Size Free Dyn Gpt -------- ------------- ------- ------- --- --- Disk 0 Online 465 GB 38 MB Disk 1 Online 10 GB 1024 KBDISKPART> select disk 1Disk 1 is now the selected disk.DISKPART> offline diskDiskPart successfully offlined the selected disk.DISKPART>Step 4Restore the LUN from Unisphere or by using naviseccli.Note: SnapCLI does not allow restores for security reasons.Step 5Mount the drive (On Windows 7, assign a letter)Restore CGsWhen restoring a Consistent Snapshot to a CG, it is possible that themember list of the current CG may be out of sync with the list of LUNs ina Consistent Snapshot. This happens when a CG is extended withadditional members.In this case, the array does not let users restore CG from a snapshot withdifferent CG members than the current member list. The CG must bemodified to match the member list of the snapshot, followed by anotherrestore attempt.Repurpose SnapshotsSome snapshots may need to be repurposed for other use. For example,when a primary LUN must be deleted, but one of its VNX Snapshotsneed to be retained.There are two ways to do that: • Migrate the SMP to another LUN before deleting the primary LUN • Detach a snapshot and then restore the primary LUN (from that snapshot) o The primary LUN may have a different HLU than SMP, or may even be presented to another host. Make sure to check where the data is provisioned. o In addition, the primary LUN has a different WWN from the SMP. So, if any of your tools or scripts are using the WWN of the SMP/primary LUN, they must be updated. VNX Snapshots White Paper 31
    • MigrationsOne of the VNX Snapshot use cases is to promote a snapshot to be atypical LUN. To do that, the snapshot must be attached, and then theSMP can be migrated to another LUN.If a migrating SMP has any snapshots associated with it (for exampleCascading Snapshots), all of them will be destroyed.Figure 29: Attached Snapshot before migrationConsider the example in Figure 29: • Host 1 is a production server running an application with PrimaryLUN1 provisioned. • Host 2 is a development server. This server must try a new version of the application on a copy of the production data. • The Administrator performs the following actions: o Takes a snapshot Snap2 from the production PrimaryLUN1 o Creates an SMP SMP Name for snapshot from PrimaryLUN1 VNX Snapshots White Paper 32
    • o Provisions SMP Name to Host 2 (for example adds SMP Name to the storage group for Host 2) o Attaches Snap2 snapshot to SMP Name o Runs SCSI rescan on Host 2 o Creates a local drive on Host 2 • At some point, SMP Name is snapped, and a Snap2.1 is created.After some time of running development code on SMP Name, it is decidedto promote it to an independent LUNThe Administrator performs the following actions: • Creates a new LUN, LUN Temp that is the same size as PrimaryLUN1. The new LUN does not have to be a pool LUN, or be in the same pool. It can be any LUN that is supported by the VNX array. • Starts a LUN migration session from SMP Name to LUN Temp o Unisphere displays a warning message that the existing SMP Name snapshots will be destroyed. Figure 30: Unisphere LUN migration warning o Administrator acknowledges the warning. VNX Snapshots White Paper 33
    • • The LUN migration runs for some time. The speed of migration depends on several factors such as the LUN priority, size of PrimaryLUN1, and array load. • Migration completes and o SMP Name Snapshot Mount Point is deleted o LUN Temp is renamed to SMP Name and retains all the SCSI attributes of the Mount Point, including WWN and even HLU ID within the storage group. o Snap2.1 is destroyed  An internal process examines the blocks used for Snap2.1 and returns them to the poolFigure 31: Migrating an attached Snapshot Mount Point to a new LUNNote: If any of the SMP Name snapshots were attached, the LUNmigration would not have started. If SMP Name had many unattachedsnapshots, they would be deleted as a result of LUN migration. VNX Snapshots White Paper 34
    • Migration considerations • When a primary LUN with SnapView snapshots is migrated to a RAID or pool LUN, all SnapView snapshots migrate to the destination LUN • When a primary LUN or attached SMP with VNX Snapshots is migrated to a RAID or pool LUN, all VNX Snapshots are deleted (migration does not start if one of several of the underlying VNX Snapshots are attached or in use)Limits • The maximum number of snapshots per primary LUN is 256. The system displays an error if a user tries to create more snapshots. The same error is displayed in the CLI. • When a pool LUN has a VNX Snapshot and a SnapView Snapshot at the same time, SnapView COFW takes priority over ROW. That means that the "old" data is copied to the Reserve LUN Pool (RLP) first, before the "changed" data is written. The data written is still placed in the proper pool space, not within the pool LUN (as it would have been if the LUN had not been a RAID group LUN.) • A snapshot taken before primary LUN (thin LUN only) expansion does not reflect the new size. Therefore, a restore from that snapshot will restore primary LUN back into the old size. • An Attached SMP can be expanded, but only if it is attached to a snapshot and is associated with a Thin primary LUN. SMPs associated with Thick LUNs cannot be expanded. VNX Snapshots White Paper 35
    • VNX Snapshot Auto-DeleteAs stated earlier, VNX Snapshots use pool space and decrease theamount of user usable space in the pool. The mechanism to controlunlimited snapshot growth was created, and dubbed Auto-DeleteManagement.The main goal of VNX Snapshot Auto-Management is not to let thesnapshots take usable space away from pool LUNs. Auto-Delete iscontrolled by the Auto-Delete policy that can be set on each pool, poolLUN, CG, and VNX Snapshot. Every Auto-Delete policy has two sets ofthresholds: a. Pool Space Thresholds (low and high) b. Snapshot Space Thresholds (low and high)The Auto-Delete Pool policy is enabled by default. However, in can beeasily disabled.Note: Only Storage Pool Auto-Delete policy is enabled by default. Thepolicy for Pool LUNs, Consistency Groups, and VNX Snapshots aredisabled by default.Figure 32: Unisphere Pool properties, showing Auto-Delete policyThe Auto-Delete policy can be enabled or disabled for the followingobjects: • Pool • LUN VNX Snapshots White Paper 36
    • • Snapshot (Regular or Consistent Snapshot) • Consistency Group • SMPWhenever a high threshold is crossed, the VNX array starts an Auto-Delete process that scans the affected pools for Snapshots that areeligible for destruction based on the Auto-Delete policy of the pools,primary LUNs, SMPs, CGs, and snapshots.Note: Attached snapshots are excluded from Auto-Delete regardless ofother settings.Disabling Auto-Delete at the pool level disables all Auto-Deleteoperations within the pool, regardless of the individualLUN/CG/snapshot settings (except for scanning for expired LUNs).Disabling Auto-Delete on a LUN, SMP, or CG, disables Auto-Delete on allsnapshots created from it regardless of the individual snapshotsettings.Snapshots are Auto-Deleted one at a time, because the system does nothave an ability to predict how many snapshots need to be deleted toreach the low threshold.Auto-Delete ThresholdsFigure 33 shows Auto-Delete thresholds.Figure 33: Storage Pool Auto-Delete ThresholdsPool Space Used ThresholdPool Space Used Threshold is a user configurable parameter thatdetermines whether the system should monitor the space used in the VNX Snapshots White Paper 37
    • Pool and Auto-Delete snapshots if required. When enabled, thefollowing thresholds are used for space monitoring. When disabled, thethreshold values are retained by the system but the pool space used isnot actively monitored.Pool Space Used Threshold is enabled by default at the time of Poolcreation.There are two Pool Space Used Thresholds: • Pool Space Used High Threshold: By default, it is set to 95% of the pool capacity. When the pool crosses the threshold, the Auto-Delete process is triggered. This process examines pool snapshots for destruction eligibility in order of age, oldest first. When eligible snapshots are found, the process starts deleting them one at a time. • Pool Space Used Low Threshold: By default, it is set to 85% of the pool capacity. This threshold must be smaller than Pool Space Used High Threshold. When this threshold is crossed, it is an indication for the Auto-Delete process to stop looking for new snapshots eligible for deletion.Snapshot Space Used ThresholdSnapshot Space Used Threshold is a user configurable parameter thatdetermines whether the system should monitor the Snapshot spaceused in the pool and Auto-Delete Snapshots if required. When enabled,the following thresholds are used for space monitoring. When disabled,the threshold values are retained by the system but the snapshot spaceused is not actively monitored.Snapshot Space Used Threshold is disabled by default at the time ofpool creation.There are two Snapshot Space Used Thresholds: • Snapshot Space Used High Threshold: By default, it is set to 25% of the pool capacity. When the pool crosses the threshold, the Auto- Delete process is triggered. This process examines the pool snapshots for destruction eligibility in order of age, oldest first, and starts deleting them one at a time. • Snapshot Space Used Low Threshold: By default, it is set to 20% of the pool capacity. This threshold must be smaller than Snapshot Space Used High Threshold. When this threshold is crossed, it is an indication for the Auto-Delete process to stop looking for new snapshots eligible for deletion. VNX Snapshots White Paper 38
    • Delete EligibilityA busy snapshot is excluded from Auto-Delete or expiration destruction.A snapshot is busy when: • It is attached to a SMP • It is involved in a restoreThe Auto-Delete settings can be set in multiple places. Use the followingtable for system rules. Pool LUN VNX Auto-Delete behavior Snapshot On On On Snapshots are subject to destruction On On Off This snapshot is exempt from destruction On Off On or Off Snapshots are exempt from destruction Off On or Off On or Off All pool Snapshots are exempt from destructionSimilar rules apply to Consistent Snapshots.Note: If a Consistent Snapshot has member LUNs in multiple pools,Auto-Delete in any of those pools can delete that snapshot unless thesnapshot or its Source CG are exempt.Auto-Delete pausedWhen Auto-Delete is unable to find enough eligible snapshots to deleteto be able to reach the Low Threshold, a warning is posted.To resolve the warning, perform one or several of the following actions: • Increase pools capacity by adding more disks to it • Manually delete snapshots • Change configuration to allow more snapshots to be automatically deleted • Change thresholdsIn some extreme cases, when deleting snapshots or failing to findeligible Snaps to be deleted, the Auto-Delete process does not getbelow the High Threshold. In that case, the Auto-Delete process stopsand posts an "Automatic Snapshot deletion paused" array error. VNX Snapshots White Paper 39
    • Figure 34: Unisphere Auto-Delete errorTo correct the error, perform one or several of the same actions as with awarning and make sure to manually restart the automatic deletionfeature in the Pool Properties dialog box. Optionally, an error conditionis lifted when Auto-Delete is completely disabled on a pool.Snapshot ExpirationEvery VNX Snapshot may have an optional expiration date. Expiredsnapshots are destroyed at regular intervals. The VNX array scans forexpired snapshots once an hour (The Auto-Delete process does notprocess destruction of expired snapshots. The destruction is handled byanother software layer.) When the expiration time is reached, thesnapshot may not be destroyed immediately. It is deleted by theprocess started at the next running interval.Setting an expiration date on a snapshot automatically disables Auto-Delete. In CLI, the user must acknowledge a warning or overwrite it with -o flag. In Unisphere, the user can set an expiration date only after Auto-Delete is disabled (unchecked).Similarly, enabling Auto-Delete for a snapshot automatically clears theexpiration timestamp for that snapshot and Unisphere displays awarning. VNX Snapshots White Paper 40
    • CLINavisphere Secure Command Line Utility, naviseccli, is updated toinclude a new command snap and extend existing lun command forVNX Snapshots.[nasadmin@~]$ naviseccli -h SPA snapUsage: snap -create -res resource [-resType type][-name snapName][-descr description] [{-keepFor keepFor|-allowAutoDelete {yes|no}}][-allowReadWrite {yes|no}][-o] snap -destroy -id snapName [-o] snap -list [{-id snapName|[-resType type][-res resource]}][{-brief|-detail}] snap -modify -id snapName [-name newName][-descr description] [{-keepFor keepFor|-allowAutoDelete {yes|no}}][-allowReadWrite {yes|no}] snap -copy -id snapName [-name newName][-o] snap -restore -id snapName [-bakName bakName][-res lunNumber][-o] snap -attach -id snapName -res lunNumber snap -detach -id snapName [-res lunNumber][-o] snap -group -create -name cgName [-res lunNumber(s)][-descr description] [-allowSnapAutoDelete {yes|no}] snap -group -destroy -id cgName [-destroySnapshots] snap -group -list [-id cgName][{-brief|-detail}] snap -group -modify -id cgName [-name newName][-descr description] [-allowSnapAutoDelete {yes|no}] snap -group -addmember -id cgName -res lunNumber(s) snap -group -rmmember -id cgName -res lunNumber(s) snap -group -replmember -id cgName -res lunNumber(s) snap -feature -infoA quick list of array maximums and total VNX Snapshot numbers isdisplayed with this command:[nasadmin@~]$ naviseccli -h SPA snap -feature -infoIs VNX Snapshots Supported: TrueMax. Snapshots: 8192Max. Snapshots Per Primary LU: 256Max. CGs: 128Max. Members Per CG: 64Max. Snapshot Mount Points: 1024Total Number of Snapshots: 42Total Number of CGs: 3Total Number of Snapshot Mount Points: 16Instead of listing CLI commands, view the collection of commands thatare helpful for everyday CLI use.Create a SnapshotTo create a snapshot, naviseccli requires the LUN ID, and not the LUNname. Be sure to flush host buffers before creating a snapshot. See 7.1Flush buffers for an example.# Look up the LUN ID, if needed.[nasadmin@~]$ naviseccli -h SPA lun -list -name Primary_LUN1 -defaultLOGICAL UNIT NUMBER 10 <== LOOK HEREName: Primary_LUN1Default Owner: SP B# Create a Snapshot, and allow it to be mounted read/write (default is no)[nasadmin@~]$ naviseccli -h SPA snap -create -res 10 -resType LUN -name Primary_LUN1_Snapshot -descr "The CLI made snapshot" -allowReadWrite yes# list a Snapshot[nasadmin@~]$ naviseccli -h SPA snap -list -id Primary_LUN1_Snapshot VNX Snapshots White Paper 41
    • Name: Primary_LUN1_SnapshotDescription: The CLI made snapshotCreation time: 03/27/12 10:54:54Source LUN(s): 10Source CG: N/AState: ReadyAllow Read/Write: YesModified: NoAllow auto delete: YesExpiration date: NeverCopy a SnapshotAs explained earlier, a copy of a snapshot does not inherit twoproperties: • Name • Allow Read/Write flag, which is set to No by defaultCreation time is inherited from the original snapshot.[nasadmin@~]$ naviseccli -h SPA snap -copy -id Primary_LUN1_Snapshot -name Primary_LUN1_Snapshot_COPY[nasadmin@~]$ naviseccli -h SPA snap -list -id Primary_LUN1_Snapshot_COPYName: Primary_LUN1_Snapshot_COPYDescription: The CLI made snapshotCreation time: 03/27/12 10:54:54Source LUN(s): 0Source CG: N/AState: ReadyAllow Read/Write: No <===== LOOK HERE. Allow Read/Write property is not copied!Modified: NoAllow auto delete: YesExpiration date: NeverCreate a Snapshot Mount PointAn SMP is a LUN-like object, and is created similar to a simple poolLUN.The -allowInbandSnapAttach property is a security feature, that letsSnapCLI from the host to attach/detach snapshots to this mount point.[nasadmin@~]$ naviseccli -h SPA lun -create -type Snap -primaryLunName Primary_LUN1 -name PrimaryLUN1_SMP1 -allowInbandSnapAttach yes -sp B# list the SMP[nasadmin@~]$ naviseccli -h SPA lun -list -name PrimaryLUN1_SMP1LOGICAL UNIT NUMBER 8155 <=== Note the LUN numberName: PrimaryLUN1_SMP1UID: 60:06:01:60:13:40:2A:00:70:5C:2C:51:1E:78:E1:11Current Owner: SP BDefault Owner: SP BAllocation Owner: SP BUser Capacity (Blocks): 20971520User Capacity (GBs): 10.000Consumed Capacity (Blocks): 8404992Consumed Capacity (GBs): 4.008Pool Name: Pool 0Raid Type: r_5Offset: 0Auto-Assign Enabled: DISABLED VNX Snapshots White Paper 42
    • Auto-Trespass Enabled: DISABLEDCurrent State: ReadyStatus: OK(0x0)Is Faulted: falseIs Transitioning: falseCurrent Operation: NoneCurrent Operation State: N/ACurrent Operation Status: N/ACurrent Operation Percent Completed: 0Is Pool LUN: YesIs Thin LUN: YesIs Private: NoIs Compressed: NoTiering Policy: Auto TierInitial Tier: Highest AvailableTier Distribution:Performance: 100.00%After the SMP is created, it could be added to a Storage Group, similar toa typical LUN:[nasadmin@~]$ naviseccli -h SPA storagegroup -addhlu -gname "Storage Group 1" -hlu 50 -alu 8155Attach a SnapshotThere are two ways to attach a snapshot: 1. Attach a snapshot to an SMP by sending a command to the SMP 2. Attach a snapshot to an SMP by sending the command to the snapshot# attach via the lun command[nasadmin@~]$ naviseccli -h SPA lun -attach -l 8155 -snapName Primary_LUN1_Snapshot# attach via the snap command[nasadmin@~]$ naviseccli -h SPA snap -attach -id Primary_LUN1_Snapshot -res 8155# Note: in both cases 8155 is the LUN ID of the Snapshot Mount PointIf a snapshot does not allow read/write access, you will receive thefollowing error:[nasadmin@~]$ naviseccli -h SPA snap -attach -id Primary_LUN1_Snapshot -res 8155The properties of this snapshot do not allow it to be attached. Modify the snapshotproperties to allow it to be attached and retry the attach operation. (0x716d802e)# To modify the Read/Write flag use this command:[nasadmin@~]$ naviseccli -h SPA snap -modify -id Primary_LUN1_Snapshot -allowReadWrite yes# And repeat attach[nasadmin@~]$ naviseccli -h SPA snap -attach -id Primary_LUN1_Snapshot -res 8155Create a Cascading SnapshotCascading snapshot is a snapshot of an attached SMP.[nasadmin@~]$ naviseccli -h SPA snap -create -res 8155 -name PrimaryLUN1_Cascading_Snapshot1# list the result[nasadmin@~]$ naviseccli -h SPA snap -list -id PrimaryLUN1_Cascading_Snapshot1 -detailName: PrimaryLUN1_Cascading_Snapshot1Description:Creation time: 03/27/12 12:54:21 VNX Snapshots White Paper 43
    • Last modify time: NeverLast modified by: N/ASource LUN(s): 8155 <===== LUN ID of the SMP (aka PrimaryLUN1_SMP1)Source CG: N/APrimary LUN(s): 10 <===== LUN ID of the Primary LUN (aka Primary_LUN1)State: ReadyStatus: OK(0x0)Allow Read/Write: No <===== We didnt specify -allowReadWrite flag at creationModified: NoAttached LUN(s):Allow auto delete: YesExpiration date: NeverDetach a SnapshotThere are two ways to detach a snapshot: 1. Detach a snapshot by sending a command to the snapshot 2. Detach a snapshot by sending the command to the SMPTo detach using a lun command, use the name of the SMP. There are nowarnings.[nasadmin@~]$ naviseccli -h SPA navi lun -detach -name PrimaryLUN1_SMP1However, when sending the detach command to a snapshot itself, thereare warnings:[nasadmin@~]$ naviseccli -h SPA snap -detach -id Primary_LUN1_SnapshotWARNING : Attempting to detach a snapshot mount point that has snapshots. The snapshotsof the mount point will be inherited by the source of the snapshot being detached.Snapshot mount point: 8154Are you sure you want to perform this operation?(y/n): yes[nasadmin@~]$ naviseccli -h SPA snap -list -id Primary_LUN1_Snapshot -detailName: Primary_LUN1_SnapshotDescription: The CLI made snapshotCreation time: 03/27/12 10:54:54Last modify time: 03/27/12 13:01:09 <===== Time when detachedLast modified by: PrimaryLUN1_SMP1_COPYSource LUN(s): 0Source CG: N/APrimary LUN(s): 0State: ReadyStatus: OK(0x0)Allow Read/Write: YesModified: Yes <===== Shows as modified, since it used to be attachedAttached LUN(s): <===== Nothing listedAllow auto delete: YesExpiration date: NeverDestroy a Snapshot[nasadmin@~]$ naviseccli -h SPA snap -destroy -id Primary_LUN1_SnapshotAre you sure you want to perform this operation?(y/n): yesList all VNX Snapshots for a LUNCheck whether the LUN belongs to a CG.[~]$ naviseccli -h SPA lun -list -l 4 -belongsToCGLOGICAL UNIT NUMBER 4Name: LB_LUNConsistency Group: USG-CG[~]$ naviseccli -h SPA lun -list -l 12 -belongsToCG VNX Snapshots White Paper 44
    • LOGICAL UNIT NUMBER 12Name: LB_LUNConsistency Group: N/ANote: The getlun command does not show the VNX Snapshotinformation.[~]$ naviseccli -h SPA getlun 4 | egrep -i "group|snap"RAIDGroup ID: N/AIf the LUN is a part of a CG, use that CG name to find the list of all LUNs:[~]$ naviseccli -h SPA snap -list -res CG_nameName: 2012-02-10 14:45:18Description:Creation time: 02/10/12 14:45:24Source LUN(s): 4,5Source CG: CG_nameState: ReadyAllow Read/Write: YesModified: NoAllow auto delete: YesExpiration date: NeverName: Backup Snapshot:2012-02-14 04:28:21Description:Creation time: 02/14/12 16:28:23Source LUN(s): 4,5Source CG: CG_nameState: ReadyAllow Read/Write: NoModified: NoAllow auto delete: YesExpiration date: NeverTo list snapshots for a single LUN (that is not a member of a CG) specifythe LUN ID or name with -res option.Create a Consistency GroupTo create a CG with two member LUNs, use this command:[~]$ naviseccli -h SPA snap -group -create -name "CG_name" -res 4,5 -descr "CG group1"List Consistency GroupsTo list all CGs on the array, use this command:[~]$ naviseccli -h SPA snap -group -listName: CG_nameDescription:Allow auto delete: YesMember LUN ID(s): 4, 5State: ReadyName: USG-CG_mountpointsDescription:Allow auto delete: YesMember LUN ID(s): 8081,8080State: Ready VNX Snapshots White Paper 45
    • Create a Consistent SnapshotTo snap a Consistent Snapshot, use the command:[~]$ naviseccli -h SPA snap -create -res CG_Name -name Consistent_SnapNote: When creating a Consistent Snapshot on a CG that has only SMPmembers, all the SMPs must be attached.Otherwise, the following error is displayed:[~]$ naviseccli -h SPA snap -create -res CG_Name -name Consistent_SnapThe snapshot of the consistency group cannot be created because some members of thegroup are unattached snapshot mount points. Attach all members of the consistency groupand retry the operation. (0x716d8063)Attach a Consistent SnapshotCLI does not allow attaching a Consistent Snapshot to multiple SMPs inone command. It is only possible to attach a Consistent Snapshot toevery SMP one by one.[~]$ naviseccli -h SPA lun -attach -name SMP1 -snapName Consistent_Snap[~]$ naviseccli -h SPA lun -attach -name SMP2 -snapName Consistent_Snap[~]$ naviseccli -h SPA lun -list -showOnly Snap -attachedSnapshotLOGICAL UNIT NUMBER 504Name: SMP1Attached Snapshot: Consistent_SnapLOGICAL UNIT NUMBER 503Name: SMP2Attached Snapshot: Consistent_Snap VNX Snapshots White Paper 46
    • SnapCLISnapCLI is the utility used on the host to manage snapshots and theirattachments to the SMPs. It does in-band (FC or iSCSI) communicationwith the array and thus does not require an IP connection to the StorageProcessor (SP).SnapCLI is similar to the ADMSNAP utility in SnapView. Both provide thesame level of security in that they can only manage snapshots of LUNsthat they have access to, based on the primary LUNs or existing SMPsexposed to the host. In other words, the array administrator sets up theprimary LUNs and/or SMPs and puts them in the host storage group andthen the host administrator may use SnapCLI to manage snapshotcreation, destruction, attach and detach for those LUNs only.Note: To run SnapCLI, run the SnapCLI command from its installationfolder, or modify the PATH to include the SnapCLI path. The default pathin Windows is C:Program FilesEMCUnisphereSnapCLIFlush buffersLike ADMSNAP, SnapCLI must be used to flush disk buffers beforecreating or detaching a VNX Snapshot. This is especially important inWindows environments.:: WindowsSnapCLI flush -o G:Create a Snapshot:: WindowsSnapCLI create -s SnapCLI_snap1 -o .PhysicalDrive1:: Or address by the drive letterSnapCLI create -s SnapCLI_snap2 -o G:Attach a SnapshotThe following command attaches a snapshot to the first SMP available.When there are many SMPs (that belong to the primary LUN), the firstavailable SMP is used (usually the one identified as the lower drive, e.g..PhysicalDriveX).:: WindowsSnapCLI attach -s SnapCLI_snap1 -fNote: When the -f option is supplied, VNX changes the -allowReadWrite property to "Yes" while the snapshot stays attached.Copy a SnapAn attached snapshot cannot be copied. Therefore, the request to copyan attached snapshot will fail. VNX Snapshots White Paper 47
    • When a snapshot is not attached, it can be copied. You must specifyboth the name of the Snap to be created and the name of the Snap to besnapped.:: WindowsSnapCLI copy -s SnapCLI_snap1_copy -b SnapCLI_snap1 -o G:Consistency GroupsOne main difference between SnapCLI and ADMSNAP is the introductionof Consistency Groups support. When creating VNX Snapshots, you canspecify the name of Consistency Group (CG) along with a list of LUNs. Ifthe specified CG does not already exist, it is created containing the LUNsspecified as members.Note: If the specified Consistency Group already exists, the existingmembers of the CG are replaced with the LUNs specified as members.The storage system maintains the CG and member LUNs persistently.:: Windows:: Create a Consistent Snapshot, and a Consistency group (if it doesnt exist)SnapCLI create -s Consistent_Snap -o T:,R: -c CG_nameSample SnapCLI batch scriptNote: SnapCLI does not support storagegroup commands. Therefore, allnecessary SMPs must be provisioned to the hosts before SnapCLI canmount any snapshots. SMPs are not required for snapshot creation.:: Windows@echo off:: Create one snapecho "Creating a snapshot for drive M:"SnapCLI create -s SnapCLI_snap_m -o M::: Create a Consistent Snap:: and a Consistency group (if it doesnt exist)SnapCLI create -s Consistent_Snap -o T:,R: -c CG_name:: Attach a single snap:: (requires 1 mount point already provisioned to the host)SnapCLI attach -s SnapCLI_snap_m -f:: Attach a Consistent Snapshot:: (requires as many mount points as number of LUNs in the CG)SnapCLI attach -s Consistent_Snap -f VNX Snapshots White Paper 48
    • VNX Snapshots vs. SnapView terms The following table shows the consolidated difference between VNX Snapshots and SnapView terminology. VNX Snapshot Definition SnapView Snapshot Point-in-time copy of a LUN2 Session Create Take a point-in-time copy of a LUN3 Start Attach Connect a snapshot to Snapshot Mount Activate Point Detach Disconnect from a Snapshot Mount Point Deactivate Primary LUN LUN4 from which the snapshot is taken Source LUN Snapshot An object that is exposed to the host Snapshot Mount Point through a storage group Restore Change a LUN data to a specific point-in- Rollback time copy Delete Delete a snapshot Stop Copy Create an identical copy of a Snapshot -- N/A -- Consistency Persistent grouping of primary LUNs or -- N/A -- Group Mount Points2 In here, besides LUNs, VNX Snapshots can be taken on a Consistency Group, or Attached Mount Point3 Same as above4 Same as above VNX Snapshots White Paper 49
    • Terminology • Consistency Group—an object that contains a list of primary LUNs or Snapshot Mount Points (but not both) that are treated as a single entity for taking snapshots. • Consistent Snapshot—a point-in-time copy of a Consistency Group. • Copy on First Write (COFW)—the technology behind SnapView Snapshots. After a snapshot is taken, new writes to the primary LUNs are delayed to enable copying old blocks to the special reserve LUN within the Reserve LUN Pool. • Logical Unit Number (LUN)—is the identifying number of a SCSI or an iSCSI object that processes SCSI commands. The LUN is the last part of the SCSI address for a SCSI object. The LUN is an ID for the logical unit, but the term is often used to refer to the logical unit itself. • Mount Point, Snapshot Mount Point (SMP)—a virtual LUN-like container. It is used to "emulate" a typical LUN, but provide the ability for hosts to write to snapshots and to change snapshots without changing LUN properties such as WWN, and often without the need to rescan SCSI bus on the client. • Redirect on Write (ROW)—the technology behind VNX Snapshots. After a snapshot is taken, new writes to the primary LUN are redirected (written) to a new location within a storage pool. • Storage processor (SP)—a hardware component that provides the processing resources to perform storage operations such as creating, managing, and monitoring storage resources. • Unisphere—a web-based management environment to create storage resources, configure and schedule protection for stored data, and manage and monitor other storage operations on VNX and VNXe systems. VNX Snapshots White Paper 50
    • Properties DetailedSnapshot propertiesEvery snapshot has the following properties: Snapshot Description User Value range property editable? Name Unique user friendly name. Yes ASCII, all printable This name can be used to characters (0x20 identify the snapshot in to 0x7E) with no management commands. The leading or trailing array will generate a unique spaces. name if it is not supplied Maximum length: during the time of snapshot 255 creation. Description User-created description. Yes ASCII, all printable characters (0x20 to 0x7E) with no leading or trailing spaces. Maximum length: 255 Creation Time The time when the snapshot Timestamp was created Last Modify The time when the snapshot Timestamp or the Time was last detached from an word "Never" SMP Last Modified The field is blank until the ASCII, all printable By first snapshot is detached. characters (0x20 After it is detached, the field to 0x7E) with no is updated with the name of leading or trailing the SMP that the snapshot spaces. was attached to. Maximum length: 64 Primary LUN Name of the source that is ASCII, all printable used to create the Snapshot. characters (0x20 to 0x7E) with no leading or trailing spaces. Maximum length: 64 State Object state from the arrays • Initializing point of view. • Ready • Faulted VNX Snapshots White Paper 51
    • Snapshot Description User Value range property editable? • Offline • Destroying Allow An indicator whether the Yes Yes/No Read/Write Snapshot may be attached to an SMP or not. The default setting is “No”. Modified An indicator that the Yes/No snapshot is or had previously been attached to an SMP. Source LUNs The SMP that the Snapshot is List currently attached to. Allow auto An indicator whether or not Yes Yes/No delete this Snapshot participates in auto-delete. Expiration The date/time that the Yes Timestamp Date snapshot will get automatically deleted (Time of day of destruction may be approximate). The default is “Never” expiring.Snapshot Mount Point propertiesEvery SMP has the following properties: SMP property Description User Value range editable? Name Unique user friendly name Yes ASCII, all printable characters (0x20 to 0x7E) with no leading or trailing spaces. Maximum length: 64 LOGICAL UNIT ID of the SMP. The array Yes Shared with all NUMBER assigns a unique LUN ID to LUN types (starts the SMP. This can be set in high similar to the GUI or CLI only at the time SnapView of creation. Snapshot LUNs) User Capacity Size of the attached snapshot. One of: • Primary LUN size if never attached VNX Snapshots White Paper 52
    • SMP property Description User Value range editable? • Current attached snapshot size • Last attached size if unattached. LUN Type Field indicating that the LUN Snapshot Attach is VNX SMP LUN State Details Details about the current ASCII state, if any WWN World Wide Name Current SP that currently owns the SPA, SPB. Owner LUN Default SP that owns the LUN by Yes SPA, SPB Owner default Auto Assign An indicator if the LUN SPA, SPB Enabled should participate in auto assignment Allocation SP Set by the array (derived from SPA, SPB the primary LUN) Auto Delete Indicator whether or not Yes Yes/No snapshots of this SMP participate in auto-delete. The default setting is “Yes”. Active Set by the array • Expanding Operation • Shrinking • Attaching • Detaching Attached User-friendly name of the Maximum length: Snapshot snapshot attached to the 255 SMP. Statistics Same as traditional LUNs, DLUs and TLUs Allow Inband Setting to enable or disable Yes • Enabled Snap Attach attach from host-based • Disabled SnapCLI.Additional pool propertiesVNX Snapshots adds the following pool properties: Pool Description User Value range property editable? VNX Snapshots White Paper 53
    • Pool Description User Value range property editable? Primary The total amount of storage Total primary Capacity that is consumed from this capacity Used pool for data written to all the primary LUNs in the pool Snapshot The total amount of storage Total snapshot Capacity that is consumed from this capacity Used pool for data written to all the snapshots in the pool Metadata The total amount of storage Total overhead Capacity that is allocated from this capacity pool to store metadata for the LUNs and Snapshots in the pool Primary The total amount of user data Total primary Subscribed that can be written to all of subscription Capacity the LUNs in the pool Snapshot The total amount of space Total snapshot Subscribed that all snapshots currently subscription Capacity consume and what they would consume if all the primary LUNs’ data was overwritten Metadata The total amount of metadata Total overhead Subscribed storage that is required to subscription Capacity support writing to the entire contents of all the LUNs in the pool Auto-Delete Indicator that the system Yes On/Off Pool Full should check the pool full Threshold high water mark for auto- Enabled delete. (Default: TRUE) Auto-Delete Pool percentage full that will Yes 0.01 - 99% 5 Pool Full High trigger snapshot auto- Water Mark deletion in the pool. Shown as a pool percentage full and also a size for convenience. (Default: 95%) Auto-Delete Pool percentage full at which Yes 0 - 98.00% 65 GUI only allows whole numbers. CLI will accept decimal places.6 GUI only allows whole numbers. CLI will accept decimal places. VNX Snapshots White Paper 54
    • Pool Description User Value range property editable? Pool Full Low auto-delete will stop Water Mark snapshot auto-deletion in the pool. This value must be less than the high water mark. (Default: 85%) Auto-Delete The state of the pool full • Idle Pool Full auto-delete process for this • Running State pool • Could not Reach LWM The “Auto-delete Pool Full • System Paused State” and “Auto-Delete • Failed Snap Used State” states will be aggregated into a single state for reporting using the GUI. Separate states for each will be reported via the CLI. Auto-Delete Indicator that the system Yes On/Off Snapshot should check the snapshot Space Used space used high water mark Threshold for auto-delete. (Default: Enabled FALSE) Auto-Delete Total percentage snapshot Yes 0.01 - 99.00% 7 Snapshot space used in the pool that Space Used will trigger snapshot auto- High Water deletion in the pool. Shown Mark as a pool percentage full and also a size for convenience. (Default: 25%) Auto-Delete Total percentage snapshot Yes 0 - 98.00% 8 Snapshot space used in the pool that Space Used will stop snapshot auto- Low Water deletion in the pool. This Mark value must be less than the high water mark. Shown as a pool percentage full and also a size for convenience. (Default: 20%) Auto-Delete The state of the Snapshot • Idle Snap Used Space Used auto-delete • Running State process for this pool • Could not7 GUI only allows whole numbers. CLI will accept decimal places.8 GUI only allows whole numbers. CLI will accept decimal places. VNX Snapshots White Paper 55
    • Pool Description User Value rangeproperty editable? Reach LWM The “Auto-delete Pool Full • System Paused State” and “Auto-Delete • Failed Snap Used State” states will be aggregated into a single state for reporting using the GUI. Separate states for each will be reported using the CLI. VNX Snapshots White Paper 56