DB2 and storage management

DB2 and Storage Management
An Uneasy Partnership

Craig S. Mullins

©2010 SoftwareOnZ
©2010 SoftwareOnZ

Author
This presentation was prepared by:

Craig S. Mullins

SoftwareOnZ LLC
15 Coventry Ct
Sugar Land, TX 77479
Tel: 281-494-6153
Fax: 281.491.0637
E-mail: craig@craigsmullins.com

2 ©2010 SoftwareOnZ

Agenda

• DBA vs. Storage Administration
• DB2 for z/OS and Storage
– Where does DB2 use storage?
– DB2 and DFSMS
– Newer DB2 Storage Features
• Mainframe Disk Storage Options
• What’s Still Missing?
• Thoughts and Best Practices


How Most Shops Manage
DB2 and Storage Administration


DBA vs. Storage Administration
From a Storage Perspective

Database Administration Storage Administration
• Capacity planning for • Capacity planning for
database objects entire environment
• Database and data • Disk and tape device
management management
• Database object interest • Data set interest
• Storage is sometimes an • Storage is always top of
afterthought mind


But Something is Missing…

• There is a gap between Database Administration,
Storage Administration (DASD) and Capacity Planning.
– Storage management can be an afterthought for the DBA…
but it shouldn’t be.
– According to Gartner, Inc. the cost of managing storage is
4-10 times the initial cost of storage acquisition.
– CAGR of disk storage was 37% between 1996 and 2007.
• Information is available to DBAs (DB2 RUNSTATS, DB2
STOSPACE, DB2 RTS, ICF Catalog, SMS Storage Groups), but it is
scattered and difficult to show the full picture.
• Any historical view has to be managed manually.
6

Are You Prepared?

Can you answer all of the following questions
about your database storage requirements:
• Do all of my databases have sufficient allocation to satisfy
business requirements?
• Why is DB2 storage growing when our business is not?
• Am I wasting any storage?
• When will more storage be required?
• How much additional storage is needed?
• What needs to be done to align the additional storage with
the DBMS?


DB2 and Storage

– DB2 and DFSMS
– Modern Storage Architecture


Tables Impact Page Size
• Tables do NOT consume storage (table spaces do)
– However, table definitions impact storage usage

– If an EDITPROC is used,
the maximum row length
is 10 bytes fewer


Table Spaces Use Disk

1

Types of Table Spaces
• Simple – max size 64 GB
– Contains one or more tables
– No new simple table spaces as of DB2 9
– Replace with universal table space partition-by-growth
• Segmented – max size 64 GB
– Contains one or more tables
– Segments between 4 and 64 (multiples of 4)
• Partitioned - up to 4,096 partitions of up to 64 GB each
– Contains one table
– Usually used for larger tables
– Replace with universal table space partition-by-range
• Universal - up to 128 TB
– Combine partitioned and segmented characteristics
– Can contain both a base and a clone table
– Two types: Partition-By-Growth and Partition-By-Range
• LOB – up to 16 TB
• XML

1

DB2 Objects and Storage
• DB2 Storage Groups: list of disk
volumes
• Table Spaces: stored on disk as at
least one VSAM LDS data set
– Could be multiple: partitioned
• Indexes: stored on disk (in an index
space) as at least one VSAM LDS
data set
• System data sets
– Active Log: stored on disk
– Archive Logs: stored on disk or tape
– BSDS: stored on disk
• Image Copy Backups: stored on disk
or tape
• Other “stuff”
– DB2 library data sets
– Temporary data sets (used by
utilities)

1

VSAM and Media Manager

DB2 uses VSAM (LDS) data sets “under the covers” to store data.
• DB2 uses VSAM Media Manager for its I/O operations.
• For every I/O, VSAM Media Manager builds a channel program and sends a
request to the I/O supervisor.

1

Multiple Data Sets per Object?

• When does DB2 utilize multiple VSAM data
sets for a table space or index?
– When the object is partitioned. Each partition will
reside in a separate data set.
• And possibly more than one per partition.
– When a data set in a segmented or simple table
space reaches its maximum size of 2 GB, DB2
might automatically create a new data set.
– When the table space is cloned.
• Each clone has its own underlying data set(s).

1

Data Set Names

catname.DSNDBx.dbname.psname.y0001.z001

DB2 database name

C (for VSAM clusters) or Instance qualifier for
D (for VSAM data components). the data set. y = I or J
(J is used when running online
Integrated catalog name REORG and CHECK utilities)1
or alias (up to eight characters).

Data set number: z = A, B, C, D, or E
Page set name: either the table space name For partitioned TS, the number is the
or the index space name. Must be unique within part number; A-E used for parts in excess
the database. of 999.
For simple or segmented TS, start with
001 and increment by one as the TS
grows past max size of 2GB.

1
For cloned table spaces, there will be I0001 and I0002 – only one of which is “active”
1

How Well Do You Track Your
DB2 VSAM Data Sets?
Picture 3

Screen shot source: zSPM
1

Where Can You Find DB2-Related
Storage Information?
• DB2 Catalog and Directory: stores metadata and control structures
• What about storage information?
– When did you last run STOSPACE and RUNSTATS?

Online DB2 catalog Tool  http://www.z-dbs.com/zcat/zcat.php?version=9
1

Storage Information in
The DB2 Catalog
• SYSTABLESPACESTATS • SYSINDEXSPACESTATS
– NACTIVE – NLEVELS
– NPAGES – NPAGES
– EXTENTS – NLEAF
– SPACE – NACTIVE
– TOTALROWS – SPACE
– DATASIZE – EXTENTS
– UNCOMPRESSEDDATASIZE • SYSINDEXES
• SYSTABLESPACE – NACTIVEF
– NACTIVEF – AVGROWLEN
– AVGROWLEN – SPACEF
– SPACEF • SYSINDEXPART
• SYSTABLEPART – PQTY
– PQTY – SQTY (or SECQTYI)
– SQTY (or SECQTYI) – STORTYPE
– STORTYPE – STORNAME
– STORNAME – PSEUDO_DEL_ENTRIES
– FREEPAGE – FREEPAGE
– PCTFREE – PCTFREE
– SPACEF – SPACEF
– EXTENTS – EXTENTS

1

DB2 and Storage

– DB2 and DFSMS

1

DB2 Storage Options

• Let DB2 manage the data sets using Storage
Groups (STOGROUPs).
– Less work for DBAs… less control over data sets.
• Let SMS manage some or all of the data sets.
– Available when you use DB2 storage groups or
when you use data sets you have defined yourself.
• Define and manage your own data sets using
VSAM Access Method Services.
– More work for DBAs… more control over data sets.

2

Storage Groups

• DB2 Storage Group • SMS Storage Group
– DB2 uses STOGROUPs for – An SMS Storage Group is a
disk allocation of the table pool of disk volumes upon
and index spaces. which SMS-managed data
– It is basically just a list of sets are placed.
storage volumes – A data set is placed on an
• Or ‘*’ for SMS appropriate volume within
– A STOGROUP can be a Storage Group depending
assigned to: upon the Storage Class,
• Databases Volume, Storage Group
• Table spaces status, and available free
• Indexes space.

2

Why Use DB2 Storage Groups?

• When a table space is created, DB2 defines the necessary VSAM data sets
using VSAM Access Method Services.
• When a table space is dropped, DB2 automatically deletes the associated
data sets.
• When a data set in a segmented or simple table space reaches its
maximum size of 2 GB, DB2 can automatically create a new data set. The
primary data set allocation is obtained for each new data set.
• DB2 can extend individual data sets as needed.
• When you create or reorganize a table space that has associated data sets,
DB2 deletes and then redefines them, reclaiming fragmented space.
– If you run REORG with the REUSE option and SHRLEVEL NONE, REORG resets
and reuses DB2-managed data sets without deleting and redefining them. If
the size of your table space is not changing, using the REUSE parameter could
be more efficient.
• When you want to move data sets to a new volume, you can alter the
volumes list in your storage group. DB2 automatically relocates your data
sets during the utility operations that build or rebuild a data set.
– LOAD REPLACE, REORG, REBUILD, and RECOVER.

2

DFSMS

• What is DFSMS?
– Data Facility Storage Management System
– Data management, backup and HSM software
from IBM mainframes.
– It combines separate backup, copy, HSM and
device driver routines into a single package.

2

DFSMS Components

DFSMS is actually multiple products; it is a suite of data
and storage management offerings.
• DFSMSdfp: Data Facility Product - provides the logical and physical input
and output for z/OS storage, it keeps track of all data and programs
managed within z/OS, and it provides data access both for native z/OS
applications and other platforms.
• DFSMSdss is a priced optional feature. It is a DASD data and space
management tool for moving and copying data.
• DFSMShsm: Hierarchical Storage Manager - a priced optional feature for
managing low-activity and inactive data. It provides backup, recovery,
migration, and space management functions.
• DFSMSrmm: Removable Media Manager - a priced optional feature for
managing removable media resources (e.g. IBM's Virtual Tape Server).
• DFSMStvs: Transactional VSAM Services – is another priced optional
feature that enables batch jobs and CICS online transactions to update
shared VSAM data sets concurrently.

2

DFSMS and DB2

• Using DFSMS, a DB2 DBA can simplify the
interaction of DB2 database creation and
storage specification. It can deliver:
– Simplified data allocation
– Improved allocation control
– Improved performance management
– Automated disk space management
– Improved data availability management
– Simplified data movement

2

Using SMS to Manage
DB2 Data Sets

Managing DB2 Data Sets with DFSMS
• The DB2 administrator can use DFSMS to achieve all the
objectives for data set placement and design.
• DFSMS has the necessary flexibility to support everything the
DB2 administrator may want.
• There is no reason to not take advantage of DFSMS for DB2
data sets.
• To achieve a successful implementation, an agreement
between the storage administrator and the DB2
administrator is required so that they can together establish
an environment that satisfies both their objectives

2

DB2 and SMS

• Defining a DB2 STOGROUP with VOLUMES (’*’) indicates
usage of SMS-managed storage.
– With SMS, the system determines data set placement.
• Minimizes DBA work.
– Requires setup work in SMS using ACS
• For example, ACS can be used to differentiate between table spaces and
index data sets and place them on different devices.
– Consider using SMS to handle the majority of DB2 data set
placement
• Perhaps using non-SMS techniques for high volume or special data sets

2

SMS Terms
• Data Classes
– This is optional, although it is usually recommended that Data Classes be assigned. Even
though it is not saved for non SMS managed data sets, the allocation attributes in the
Data Class are used to allocate the data set.
• Storage Classes
– Data sets use a Storage Class to qualify for SMS management. Here GUARANTEED SPACE
is specified, along with availability, performance, and accessibility characteristics.
• Management Classes
– This is used for migration to level 1 and level 2 with or without backup, and indicates if
there should be no HSM management (backup or migration). It also includes expiration
of data sets and space release/compaction.
• Storage Groups
– The Storage Group contains volumes that satisfy the service requirements of the data
sets allocated to them. They can handle more than one type of data. Separate Storage
Groups should be defined for production table spaces, active logs, other production
data, and non-production data.
• ACS (Automatic Class Selection)
– ACS routines assign data sets to SMS storage classes. For example, indexes can be
assigned to one SMS storage class and table spaces to a different SMS storage class.

2

DBA “Historical” Worries

• Extreme data placement
– VCAT-defined data sets for table spaces & indexes
• Managing DB2 storage groups
– Carefully associating volumes to STOGROUPs
• Extensive separation of data sets
– Examples
• careful placement to avoid contention
• always putting indexes on separate devices from data

2

User-Defined VSAM?

With STOGROUPs:
• Less knowledge of VSAM and AMS is required
• DB2 manages external storage
(Data set deletion done by DROP TABLESPACE)
• Can ALTER primary and secondary allocation quantities
• Can switch to user-managed VSAM
• Can switch to other STOGROUPs

With user-defined VSAM files:
• More flexibility through the larger parameter set of AMS
• User-managed external storage
(including deletion of the data set)
• Can switch to STOGROUP-managed data sets

3

DB2 STOGROUPs

• Most shops that have not migrated to SMS use
DB2 STOGROUPs for DB/TS/IX creation.
• STOGROUP issue:
– Up thru V9: the list of volumes in the STOGROUP is
used “in that order” when allocating space
• VOLUMES(DV06, DV01, DV07)
– V10: the order “goes away” because there are no
more links in the DB2 Catalog

3

Reducing Extents

• Modify PRIQTY / SECQTY and REORG
• Storage Administrators have other methods of
reducing extents that (perhaps) can be quicker
and/or easier:
– DFSMShsm MIGRATE and RECALL functions
– DFSMSdss COPY or DUMP and RESTORE functions
– DEFRAG with the CONSOLIDATE keyword
– Other products: e.g. Real Time Defrag

3

Data Set Placement?

• The new disk architectures, with concepts like
log structured files and with cache in the
gigabyte sizes, have a noticeable impact on
database physical design considerations.
• Conventional database design rules based on
data set placement are becoming less
important and can be ignored in most cases.

3

DB2 and Storage

– DB2 and DFSMS

3

Modern Storage Architecture
Disk… Tape… Array…

TS3400 Tape Library

IBM DS8700 Disk

TS3500 Tape Library
EMC Symmetrix Disk

3

A Disk is But a Disk?

• Mainframe disk, or DASD, is usually equated to a 3380 or
3390. In other words, physical hardware devices with a one-
to-one relationship between a disk drive and a volume. The
logical view is broken down as:
– Track size, or the number of bytes per track.
• 47476 for 3380
• 56664 for 3390
– Capacity, or the size of the device, in terms of number of tracks or
gigabytes.
– Device address, sometimes called device number, which is a thread
onto which I/O operations are serialized by the operating system
• Today these physical devices are replaced by disk arrays.
– An array is the combination of two or more physical disk storage
devices in a single logical device or multiple logical devices.

3

From RAMAC (RVA) to ESS to DS
• The RAMAC Virtual Array (RVA) came first for the mainframe and it was based on
virtual disks that emulated 3380s and 3390s.
– There is no fixed physical to logical mapping. The RVA dynamically maps functional
volumes to physical drives. This mapping structure is contained in a series of tables stored
in the RVA control unit.
– RVA was OEM'ed from Storage Technology Corp (now part of Oracle).
• The ESS (Shark) followed when the STK OEM agreement expired.
– IBM technology; scalable from 420GB to 55.9 TB
– It offered improved performance (especially for prefetch and DSS)…
– But it lacked the virtual capability, at first.
• The DS8000 employs virtualized disk. Adds additional functionality for:
– Storage Pool Striping - a method of improving performance by allocating capacity to a
logical volume such that the capacity is spread over the set of ranks in the logical volume's
extent pool.
– Thin Provisioning – a method of configuring one or more logical volumes such that
capacity for data stored on the logical volume is not allocated until the data is written.
– Quick Initialization - dynamically initializes logical volumes when they are created or
expanded allowing logical volumes to be configured and placed online more quickly
– Capacity scales linearly from 1.1 TB up to 192 TB (up to 320 TB with turbo models).

3

Disk Arrays: The Bottom Line

Although the RVA, ESS, and DS8000 all work with logical disks that
map to physical locations, they are three different architectures and
are not the same type of hardware. But there are similarities:
• They use RAID and
therefore are virtual. 3390 Model Cylinders Capacity
• Data is spread across 1 1,113 946 MB
multiple physical disks in 3 3,339 2.83 GB
the array. 9 10,107 8.51 GB
• Each I/O operation takes 27 32,760 27.84 GB
place to, or from, several 54 65,520 55.68 GB
physical disks.
• They emulate devices and Today’s disk arrays still emulate
map logical disks to physical the 3390 track architecture.
locations.

3

What is RAID?
• Redundant Array of Independent Disks
• The basic idea of RAID is this:
– Multiple disks configured together into an array.
– The array is perceived by the system to be a single disk
device.
– Hot-swappable drives improve availability
– A drive can be replaced while the array is up & running.
• There are many levels of RAID technology
– Each delivers different levels of fault-tolerance and
performance.
– Examples on next slide…

3

RAID Levels

(DS8000 and some ESS use RAID10)

Source: Advanced Computer & Network Corporation - http://www.acnc.com/04_00.html
4

DS8000: RAID10

• The IBM DS800 disk array is a RAID 10 implementation.
– RAID10 is implemented as a striped – Under certain circumstances,
array whose segments are RAID 1 RAID 10 array can sustain
arrays. multiple simultaneous drive
– RAID 10 has the same fault tolerance failures.
as RAID level 1. – Excellent solution for sites
– RAID 10 has the same overhead for that would have otherwise
fault-tolerance as mirroring alone. gone with RAID 1 but need
– High I/O rates are achieved by striping some additional performance
boost.
RAID 1 segments.

4

Popular Modern Disk Arrays

• EMC Symmetrix
• EMC V-MAX
• EMC DMX
• Hewlett Packard XP24000/XP20000 Disk Array
• Hitachi Data Systems Lightning
• Hitachi Data Systems Universal Storage Platform
• IBM System Storage ESS (Shark)
• IBM System Storage DS6000
• IBM System Storage DS8000
• Sun StorageTek V2X4f

4

What About Disk Cache?

• Data is written from DB2 buffer pools to “disk” based
on your buffer pool and checkpoint settings.
– Deferred Write Threshold (DWQT) is reached when this
pct. of the buffer pool is allocated to unavailable pages
(updated or in use). DB2 schedules write I/Os to
externalize data pages to disk.
– Vertical Deferred Write Threshold (VDWQT) is reached
when this pct. of the buffer pool is allocated to unavailable
pages of a single one data set.
– Checkpoint Frequency (CHKFREQ DSNZPARM) sets how
often a system checkpoint is taken (in minutes or log
records); data is “written” to disk at this point (among
other things)

4

So What Happens When
DB2 Writes to Disk?

• When DB2 writes to disk…
– DB2 destages updated data to the disk cache.
– DB2 treats this as a disk write, even though the write is to
cache.
– The data may or may not remain in the buffer pool
depending on why the data was destaged (DWQT, VDWQT,
CHKFREQ).
– Data is also written to the NVS (Non Volatile Storage) part
of the disk controller that is battery backed.
• Even if the disk crashes, no data is lost.
– Based on disk thresholds, cache destages data back down
to disk.

4

Some z Storage Terminology

• ESCON (Enterprise Systems Connection) is a data
connection created by IBM. It was used to connect
mainframe computers to peripheral devices such
as disk storage and tape drives.
• FICON (Fibre Connectivity) is the IBM proprietary name for
the ANSI FC-SB-3 Single-Byte Command Code Sets-3 Mapping
Protocol for Fibre Channel (FC) protocol. It is a FC layer 4
protocol used to map both IBM’s antecedent (either ESCON or
parallel) channel-to-control-unit cabling infrastructure and
protocol onto standard FC services and infrastructure.
– FICON has replaced ESCON in current deployments because of
FICON's technical superiority
• Higher performance and lower cost.
• MIDAW (Modified Indirect Address Word) is a technique for
virtual I/O addressing
4

MIDAW

• MIDAW name stands for “modified IDAW.”
– An IDAW (indirect address word) is used to specify data
addresses for I/O operations in a virtual environment.
– This improvement is available as of the System z9™.
• MIDAW is a hardware channel enhancement that
improves sequential access speed substantially for 4
KB page sizes.
• MIDAW improves FICON performance, especially
when accessing DB2 databases, by reducing channel
utilization and increasing throughput for parallel
access streams.

4

MIDAW and Prefetch

Source: IBM RedPaper (redp4201)
How does the MIDAW Facility Improve the Performance of FICON Channels Using DB2 and other workloads?
4

MIDAW and the Log

4

MIDAW & DB2: More Details

4

DB2 and Storage

– DB2 and DFSMS

5

Newer DB2 Storage Features

• Extents
– Sliding Scale Extent Allocation
– Extent Consolidation
• Variable CI Size
– Page size = CI size
• CLONE Tables
• As of V9, DB2 STOGROUP can define/alter SMS
constructs
– MGMTCLAS
– DATACLASS
– STORCLAS
• DSNZPARMs
5

What About Extents?

• For SMS-managed data set you can have up to
123 extents on each of 59 volumes.
– As of z/OS 1.7.
• So the limit is 7,257 extents for a data set;
• Instead of the 255 we’ve been used to for some time.
– To enable this, modify the DFSMS Data Class to set
the Extent Constraint Removal to YES.

5

OK, But Do Extents Still Matter?

Some folks think:
• “With RAID/modern storage devices and new DB2 & z/OS
features, extents are no longer anything to worry about.”

This is not exactly true:
• The latest extent management features only work with SMS-
managed data sets, so if you are user-managed old rules apply!
• For SMS-controlled data sets extents can still impact
performance.
– Each extent on a disk file has different control blocks
controlling access
– Elapsed time can increase if there is heavy insert activity
– Example:
• A program inserting 1m rows & using sliding extents with a very low
initial size doubled elapsed time compared to 1 extent
5
3 • May be caused by the allocation of each new dataset ©2010 SoftwareOnZ

Sliding Scale Extent Allocation

As of V8, DB2 can allocate secondary extents automatically
• Enabled by setting MGEXTSZ to YES
(DSNZPARM)
– Default is NO for V8
– Changed to YES automatically when you
upgrade to DB2 9
• Extent sizes allocated gradually increase
• Maximum Extent size is based on DSSIZE
– Up to 16 GB the largest secondary extent size
is 127 Cylinders
– 32 GB & 64 GB the largest secondary size is
559 Cylinders

5

Sliding Scale Extent Allocation

• DB2 uses a sliding scale for secondary extent allocations of
table spaces and indexes when:
– You do not specify a value for the SECQTY option of a CREATE
TABLESPACE or CREATE INDEX statement
– You specify a value of -1 for the SECQTY option of an ALTER
TABLESPACE or ALTER INDEX statement.
• Otherwise, DB2 uses the SECQTY value for secondary extent
allocations, if one is explicitly specified (and the SECQTY
value is larger than the value that is derived from the sliding
scale algorithm).
• If the table space or index space has a SECQTY greater than
0, the primary space allocation of each subsequent data set
is the larger of the SECQTY setting and the value that is
derived from a sliding scale algorithm.

5

The Sliding Scale Algorithm

• If you do not provide a value for the secondary space allocation quantity,
DB2 calculates a secondary space allocation value equal to 10% of the
primary space allocation value and subject to the following conditions:
– The value cannot be less than 127 cylinders for data sets that range in initial
size from less than 1 GB to 16 GB, and cannot be less than 559 cylinders for 32
GB and 64 GB data sets.
– The value cannot be more than the value that is derived from the sliding scale
algorithm.

• The calculation that DB2 uses for the secondary space allocation value is:

Actual secondary extent size = max ( 0.1 × PRIQTY, min ( ss_extent, MaxAlloc ) )

• In this calculation, ss_extent represents the value that is derived from the
sliding scale algorithm, and MaxAlloc is either 127 or 559 cylinders,
depending on the maximum potential data set size. Secondary space
allocation quantities do not exceed DSSIZE or PIECESIZE clause values.

5

Extent Consolidation

• Extent Consolidation
– Requires SMS-managed STOGROUPs
– If new extent is adjacent to old, they will be
merged together
– Some extents may end up being larger than the
PRIQTY or SECQTY specification(s)
– Introduced in z/OS 1.5

5

Variable CI Size
• Beginning in Version 8, DB2 can define data sets with variable VSAM control intervals.
– Prior to Version 8, DB2 defined all data sets with 4K CI size.
• One of the biggest benefits of this change is an improvement in query processing
performance.
• The VARY DS CONTROL INTERVAL parameter on installation panel DSNTIP7 (DSVCI
DSNZPARM) allows you to control whether DB2–managed data sets have variable VSAM
control intervals:
– YES - indicates that a DB2–managed data set is created with a VSAM CI that corresponds to the
size of the buffer pool that is used for the table space. This is the default value.
– NO - indicates that a DB2–managed data set is created with a fixed VSAM CI of 4 KB, regardless
of the size of the buffer pool that is used for the table space.

5

CLONE Tables

• This is not the place for a comprehensive discussion of cloning but…
– Basically, cloning creates a table with the exact same attributes as a table that
already exists, except that it has no data.
– It is created using the ALTER TABLE SQL statement with the ADD CLONE
parameter.
– The clone table is created in the same table space as the existing table.
• But in a different VSAM data set.
– After creating the clone table you can do whatever you want to do with it.
LOAD it, INSERT rows to it, etc.
– When the clone is ready to become the base table it is exchanged with the
base table. This is done using the EXCHANGE SQL statement.
– After running an EXCHANGE the clone becomes the
“real” table and the previously “real” table becomes
the clone - - and you can repeat the process.
• Bottom Line
– You’ll need more storage to manage clones.

5

DB2 V9 STOGROUPs

• If the data set that is associated with the storage group is not managed by
Storage Management Subsystem (SMS), VOLUMES must be specified.
• Asterisks are recognized only by SMS.
• Having DB2 select the volume requires non-SMS usage or assigning an
SMS Storage Class with guaranteed space.
– However, because guaranteed space reduces the benefits of SMS allocation, it
is not recommended.
• If one or more of the DATACLAS, MGMTCLAS, or STORCLAS clauses are
specified, VOLUMES can be omitted. If the VOLUMES clause is omitted,
the volume selection is controlled by SMS.
• Verifying the existence of volumes and classes: When processing the
VOLUMES, DATACLAS, MGMTCLAS, or STORCLAS clauses, DB2 does not
check the existence of the volumes or classes or determine the types of
devices that are identified or if SMS is active. Later, when the storage
group allocates data sets, the list of volumes is passed in the specified
order to Data Facilities (DFSMSdfp).

6

DSNZPARMs

• SEQCACH BYPASS | SEQ
– Original meaning (for 3390) was whether DB2 I/O should
bypass the disk cache, but the meaning is different now
– BYPASS - the disk will perform Sequential Detection
– SEQ - creates an explicit Prefetch request
• Recommendation: set to SEQ for improved performance
• SEQPRES YES | NO
– Similar to SEQCACH, but for DB2 LOAD and REORG utilities
– If set to YES the Cache is more likely to retain pages for
subsequent update, particularly when processing NPIs
– Recommendation: set to YES

6

DSNZPARMs

• MGEXTSZ YES | NO
– Whether or not DB2 will manage Sliding Extents?
– Note: the default changed to YES in DB2 9 (it was NO in DB2 V8)
• TSQTY 0 and IXQTY 0
– Sets default object sizes if USING clause omitted
– Default values use 1 cylinder except for LOBs which use 10 cyls
• DSVCI YES | NO
– Whether to use variable CI sizes
– Note this is turned on by default when you install V8
• SVOLARC YES | NO
– YES means allocate a single volume for disk based archives
• Saves space if you use SMS guaranteed space option

6

DSNZPARMs

SMS Related DSNZPARMs
• SMSDCFL
– Specifies a DFSMShsm data class for table spaces.
– If you assign a value to SMSDCFL, DB2 specifies that value
when it uses Access Method Services to define a data set
for a table space.
• SMSDCIX
– Specifies a DFSMShsm data class for indexes.
– If you assign a value to SMSDCIX, DB2 specifies that value
when it uses Access Method Services to define a data set
for an index.

6

Wrapping It All Up

• Questions to ask yourself
• Thoughts and Ideas

6

Storage Problems

• Out of space
• Allocation issues
• Growing very rapidly
• Too many extents
• Approaching thresholds
• Orphaned image copies
• My index keeps growing!

6

Can You Answer These Questions?

• My volumes are SMS managed; how can I tell
what my volume names are, how much space
I have left, and how much space I have used?
• Can you rely on the information in the RTS?
– The EXTENTS column in the RTS will be updated
only when an update or applicable utility is run for
the object. A simple start after extent reduction or
a read based on SELECT will not update the
EXTENTS column (same issue as the catalog).

6

Examples of DB2 Storage “Things”
You Should Be Monitoring
• Space display and monitoring of a DB2 system.
• Space display and monitoring of Databases.
• Space display and monitoring of the Tablespaces (and Indexes).
• Display and monitoring of the Storage Groups and the associated volumes of a
DB2 system. (Data, Workfile, Image Copies, Logs, Archives, Sort/Work etc.)
• VSAM display of all Tablespaces and Indexes (Used, Allocated, Primary and
Secondary Quantity, Volumes) and monitoring of Extents (physical and logical).
• Display of the Linear Page Sets of Tablespaces and Indexes, that reach their
maximum size (part. objects, DBSIZE) resp. the maximum number of datasets (non-
part. objects, PIECESIZE).
• Intelligent HSM Migration of Image Copy Backup Data Sets, that are not used
for a local recovery (to CURRENT), as well as datasets older than the last Full Image
Copy (Dual and Remote Backups)
• Delete of Image Copy Backup datasets of a DB2 system that are no longer
needed because of DROP, DROP/CREATE or MODIFY TABLESPACE (‘orphaned‘, not
listed in SYSIBM.SYSCOPY).

6

Allocated Space

Picture 3

Screen shot source: zSPM

6

Growth of DB2 & DB2 Objects
Picture 3

Picture 3

Screen(s) shot source: zSPM
6
9
6

My Index Keeps Growing… Help!

Problem: My index keeps on growing and tripping extents, even
after deletes. What gives? How can I control the extent growth?
• For an index, deleted keys are marked as pseudo deleted.
– Actual cleaning up occurs only during certain processes (for example,
before a page split).
– This can cause indexes to “grow” even when the data technically is not.
– It can also result in high CPU cost for index scans.
• Whenever an index scan is invoked, DB2 will scan all entries in the index
including pseudo-deleted entries that have yet to be removed.
• Calculate the percentage of pseudo-deleted RIDs using
information in SYSINDEXPART:
– (PSEUDO_DEL_ENTRIES/CARDF)*100
• Reorg the index when pct of pseudo-deleted entries is:
– Greater than 10% for non Data Sharing
– Greater than 5% for Data Sharing.
7

What About Compression?

• CPU vs. I/O
• DSN1COMP
– Anything less than 40%, is probably not worth
doing.
• Compression dictionary is above the 2GB bar
as of V8
– Allows for more table spaces that can be
compressed

7

Best Practices

• Keep up-to-date on DB2/storage functionality.

• Perform regular and proactive monitoring.

• Build alerts to inform you of problems,
shortages, and potential errors.

• When possible, take automated action in case
of shortages, potential errors, superfluous
data sets, etc.

7

References

• Advanced Computer & Network Corporation, RAID.edu, http://www.acnc.com/04_00.html
• IBM Manual, DFSMS Introduction (SC26-7397)
• IBM Manual, DFSMS Storage Administration Reference (for DFSMSdfp, DFSMSdss, DFSMShsm) (SC26-7402)
• IBM Manual, DFSMS Implementing System-Managed Storage (SC26-7407)
• IBM RedBook, Storage Management with DB2 for OS/390 (SG24-5462)
• IBM RedBook, Maintaining Your SMS Environment, (SG24-5484
• IBM RedPaper, Disk Storage Access with DB2 for z/OS (redp4187))
• IBM RedPaper, DB2 for OS/390 Performance on IBM Enterprise Storage Server (redp0026)
• IBM RedPaper, How does the MIDAW Facility Improve the Performance of FICON Channels Using DB2 and
other workloads? (redp4201)
• IBM System z Storage Management Strategy
ftp://ftp.software.ibm.com/software/systemz/pdf/whitepaper/IBM_System_z_Storage_Management_Strategy_v1.1.pdf
• IBM DS8000 Storage Virtualization Overview
ftp://public.dhe.ibm.com/common/ssi/sa/wh/n/diw03020usen/DIW03020USEN.PDF
• Iczkovits, John, DB2 and Storage Management: a Guide to Surviving a Perfect Marriage, SHARE February
2008
• Mullins, Craig S., DB2 Developer’s Guide, 5th edition, Indianapolis, IN: SAMS Publishing: ISBN 0-672-32613-4
• Smith, Ellin, DB2 UDB on z/OS Using EMC Symmetric Storage Systems Solution Guide, EMC Corporation,
ISBN 9781604613407
• Thomas, Steve, Do Extent Numbers Really Matter Any More?, IDUG Europe 2008, Session A14
• Toigo, Jon William, The Holy Grail of Data Storage Management, Upper Saddle River, NJ: Prentice-Hall: ISBN
0-13-013055-9

7

Questions?

7

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7

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