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SAN Basics for DBAs

Joey D’Antoni Central Pennsylvania User GroupNovember 13, 2012

About Me

Principal Architect SQL Server at Comcast Cable Blog: joedantoni.wordpress.com Twitter: @jdanton Email: jdanton1@yahoo.com

Storage

Understanding Storage Types SSDs RAID Levels Components of a SAN SAN Benefits SANs and DR Summary

Storage

Different Kind of Storage

Hard Drive Components

Caching

Almost all hard drives (SAN, Direct Attached) 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!

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

Why is storage the bottleneck?

Memory versus Hard Drives

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

SSDs (Solid State Drives)

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

SSDs are Expensive

List Prices From Fusion-IO160GB 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

SANs and SSDs

More to come later!

RAID

RAID—Redundant Array of Independent Disks

Hard Drives Will Fail, RAID is what gives you protection from that

RAID 0

RAID 0, Don’t Do This

From a major virtualization vendor benchmark

RAID 0

No data protection at all

Best performance If you lose one disk,

you lose it all As you add disks

risk increases

RAID 1--Mirroring

Mirroring No increase in

write performance Read

performance is increased

50% Capacity Loss

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

*Caveat

RAID 1+0 (10) Mirrored Striping

Best performance Requires 4 or more

drives Only 50% of actual

capacity is used

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!!!

Storage Area Network

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

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)

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—Cable connection to SAN IOPs—I/O Operations Per Second—the way

your SAN admin measures performance

iSCSI vs Fibre Channel

iSCSI is cheaper, and in smaller shops your network admin can manage the switches

Over 10G Ethernet iSCSI is faster, unless… 16 GB FC is still uncommond

Fiber is more susceptible to breakage, but currently more common

Note—all SAN components must be the same speed, or network traffic reverts to slowest in chain

Multi-Pathing

How your SAN admin sleeps at night!

Make sure your databases servers are multi-pathed

SAN Throughput

1 GB iSCSI

4 GB FC

8 GB FC

10 GB iSCSI

0 200 400 600 800 1000 1200 1400

Max Mb/S

Max Mb/S

What are the Benefits of a SAN

Expand Capacity easily and on the fly High availability Disaster Recovery

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

SANs and DR—Block

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

SAN Replication

Shared Environment vs Dedicated Environment

SANs are Multi-Tenant

You don’t want to share disks with the Exchange server

File servers are a decent partner for database servers

But….

If you have are on a new SAN

Most of the previous slides, don’t matter This technology on applies to really high end,

enterprise-class storage arrays IBM, EMC, Hitachi

EMC VMax Fast DP

Allows for dynamic moves of disk from faster to slower disks (Fibre channel to SATA), or slower to faster (FC to SSD)

Totally dynamic, and seamless to servers Moves data in 768k extents Your SAN admin doesn’t know where your

data is

FAST VP

SSD SSD SSD

15K Fibre Channel 15k Fibre Channel 15k Fibre Channel

10K SATA 10K SATA 10K SATA

Log

Data

What does this mean for the DBA?

Overall—don’t worry too much about—the technology is solid

Make sure your transaction logs are in a group that can not go to SSD.

A lot of what we did in the past, changes with this technology

Test Your SAN

Good free tools available like SQLIO Never run this on a production server (and

warn your SAN admin)

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

Questions?

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Contact Info

Twitter: @jdanton Email: jdanton1@yahoo.com Blog (slides): joedantoni.wordpress.com