1.
SAN Basics for DBAs
Joey D’Antoni
November 5, 2011

2.
About Me
 Senior SQL Server DBA at Comcast
 Blog: joedantoni.wordpress.com
 Twitter @jdanton
 Email jdanton1@yahoo.com
11/7/2011
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3.
Storage
 Understanding Storage Types
 A little bit about SSDs
 RAID Levels
 Components of a SAN
 SAN Benefits
 SANs and DR
 Summary

4.
Storage

5.
Different Kind of Storage

6.
Hard Drive Components

7.
Caching
 Almost all hard drives (SAN, standalone)
have some form of caching (RAM in front of
storage)
 For SQL Servers—make sure you have a
battery backed cache—if you don’t and
power fails—you will lose data!

8.
Why is storage the bottleneck?

9.
Disk Drives
 Hard Drives can only spin at 15,000 RPM.
 Hard Drive Performance has improved
approximately 50x
 Have grown in capacity
 During the performance improvement CPU
speed increase 5521x

10.
Latency
 ―Disk latency is around 13ms, but it depends on the
quality and rotational speed of the hard drive. RAM
latency is around 83 nanoseconds. How big is the
difference?
If RAM was an F-18 Hornet with a max speed of 1,190
mph (more than 1.5x the speed of sound), disk access
speed is a banana slug with a top speed of 0.007 mph.‖
--credit Christian Paredes Blue Box Group

11.
CPU and Disks
 As CPUs have gotten faster they have the
ability to drive more IOPs.
 Modern CPUs are so powerful they can
saturate a 10 GB connection with I/O
requests—your disks can’t possibly keep up

12.
SSDs (Solid State Drives)

13.
SSDs are Fast
 Much faster on random reads and writes
 At least 5x better performance, often much more
 Up to 350x faster on seeks
 Not nearly as much of difference on
sequential reads and writes

14.
SSDs are Expensive
 List Prices From Fusion-IO
160GB SLC ioDrive - $8495
320GB SLC ioDrive - $15495
320GB MLC ioDrive - $7495
640GB MLC ioDrive - $11495
320GB SLC ioDrive Duo – 16,990
640GB SLC ioDrive Duo - $30,990
640GB MLC ioDrive Duo - $14,990
1.28TB MLC ioDrive Duo - $22,990
 These are really great for TempDB

15.
RAID
 RAID—Redundant Array of Independent
Disks
 Hard Drives Will Fail, RAID is what gives you
protection from that

16.
RAID 0

17.
RAID 0, Don’t Do This
 From a major virtualization vendor
benchmark

18.
RAID 0
 No data protection
at all
 Best performance
 If you lose one disk,
you lose it all
 As you add disks
risk increases

19.
RAID 1--Mirroring
 Mirroring
 No increase in
write performance
 Read
performance is
increased
 50% Capacity
Loss

20.
RAID 5—Striping (What you SAN Admin Wants)
 Maximum Capacity
 Big Write Penalty—
gets worse as more
disks are added
 Not good for highly
transaction
databases
 BAARF

21.
RAID 1+0 (10) Mirrored Striping
 Best performance
 Requires 4 or more
drives
 Only 50% of actual
capacity is used

22.
Summary of RAID Levels
 Ask for RAID 10 for Everything (you won’t get
it)
 Make sure your TempDB and Logs are on
RAID 10
 NEVER USE RAID 0!!!

23.
Storage Area Network

24.
What is a SAN?
 Basically a specialized computer for storage
 Computer, Switches and Hard Drives
 Not a performance device
 Can be used for redundancy and DR
purposes
 Will serve many servers—so critical piece of
your infrastructure

25.
SAN Components
 HBA (Fibre) Card—Connects your server to SAN
via Fiber Optic cable
 iSCSI Card—Ethernet Card connecting server to
SAN
 Switch—Either fibre or ethernet switch
connecting server to SAN
 SAN head unit—Controls processing, RAID
levels
 Disk Array—The physical array behind your SAN
(a bunch of hard drives)

26.
iSCSI vs Fibre Channel
 iSCSI is cheaper, and in smaller shops your
network admin can manage the switches
 Over 10G Ethernet iSCSI is faster, but that is still
uncommon
 Fiber is more susceptible to breakage, but
currently more common
 Fibre is faster, generally
 Note—all SAN components must be the same
speed, or network traffic reverts to slowest in
chain

27.
Multi-Pathing
 How your SAN
admin sleeps at
night!
 Make sure your
databases
servers are
multi-pathed

28.
SAN Benefits
 Expand Capacity easily and on the fly
 High availability
 Disaster Recovery

29.
SANs and DR
 WARNING!—Don’t try this unless you have a
real budget and a good SAN admin
 Most SANs vendors have as an option SAN
replication
 Allows for multi-site failover
 Multi-site clustering fully supported in SQL
Server 2012
 Expensive—requires fiber connection
between sites and expensive software

30.
SAN Terms
 LUN—Logical Unit Number, but in practical
terms, what your SAN admin will call a disk
that he presents to your server
 Fibre Channel—Fiber Optic connection to
SAN
 HBA Card—Card that plugs into your server
to connect it to the SAN
 IOPs—I/O Operations Per Second—the way
your SAN admin measures performance

31.
SANs and SQL Server—What to ask for
 TempDB absolutely needs its own disk (and
you should have multiple TempDB files)
 Logs should be on a separate disk from data
files
 Ideally separate system and user DBs
 If shared instance, put split high utilization
DBs onto separate disk devices

32.
Shared Environment vs Dedicated
Environment

33.
SANs are Multi-Tenant
 You don’t want to share disks with the
Exchange server
 File servers are a decent partner for
database servers

34.
Test Your SAN
 Good free tools available like SQLIO
 Never run this on a production server (and
warn your SAN admin)

35.
Summary
 RAID 0 is bad
 Hard Drives will always be the bottleneck
 Be nice to your SAN admin—ask for RAID 10
 Split your SQL files across many disks
 SSDs are fast, but pricey

36.
Questions?

37.
Contact Info
 Twitter: @jdanton
 Email: jdanton1@yahoo.com
 Blog (slides): joedantoni.wordpress.com