1 © copyright 2008 emc corporation. all rights reserved. symmetrix capacity planning and...

1© Copyright 2008 EMC Corporation. All rights reserved.

SymmetrixCapacity Planning and Performance Aspects

Bob RauTechnical Business ConsultantSymmetrix Champion, SPEED, CSPEEDEMC Corporation


Topics

Capacity Planning (from the Symmetrix side)

Disk drives How fast? How big? How much work do they do? Utilization

Front-end ports Or is it CPUs? Or boards?

How about the back-end?

Performance Aspects (from the Symmetrix side)

Almost everything counts

But a few things don’t!

Performance Aspects (from the server side)

Tuning your server to match your storage


Capacity Planning – Disk Drives

How Fast?

15K Around 50% more cost About 30% more work If you have to have that 30% you have to have 15K drives

10K Pretty darn good Cache memory can mask the slower speed from the host (sometimes)

7.2K Slower? Some workloads will thrive on these drives

Flash Drives (SSD) Faster than a speeding bullet, able to leap over tall buildings, but…. You probably can’t afford too many You need to manage them carefully You need the right type of workload



How Big?

The size of the drive doesn’t matter (usually)

Within the same speed most capacities perform the same

10K: 73 GB, 146 GB, and 300 GB are all the same 400 GB drives are a little better

15K: 73 GB, 146 GB are all the same 300 GB drives are a little better

7.2K: all of the SATA II drives are the same

Flash Drives: 73 GB and 146 GB are the same

So the actual important question is:

How much work can they do?



How much work can they do?

The important measure is “SCSI commands/second”

This includes all of the things disk drives do including Reading Writing Moving the heads Housekeeping Parity calculations Etc.

FD 15K 10K 7.2K

5,000 240 180 95

Drive type

SCSI commands/sec(if you are really good)

5,000 190 140 80SCSI commands/sec(plan on these numbers)

Be careful…. This is at 100% utilization!

DMX arrays only



What about % utilization?

With a brand new Symmetrix EMC likes to target 35% to 40% disk drive utilization

When utilization goes above 70% performance can become erratic

With certain workloads (like backups) there is nothing wrong with 100% utilization

< 30% 50% 70%

x 2x 3x

Utilization

Disk drive response time


Capacity Planning – Front-End Ports

What’s the most important part of the front-end??

Front-end boards almost never matter

Front-end ports are very important Workload on the port Ensuring high availability Restrictions on fan-in and fan-out Restrictions on LUN counts

Front-end CPUs are the truly controlling factor


Capacity Planning – Back-End Boards

Most of the time back-end boards are not a factor – except…

When there is a lot of remote replication workload

When there is a lot of Raid-6

When the loops get above 45 devices

When you are configuring Flash Drives


Performance Aspects – from the Symmetrix

Utilization numbers are always important

Utilization numbers above 70% cause erratic and poor performance

Modern storage arrays are designed to ride through brief performance spikes

One or two minute spikes are brief

15 minute spikes are forever!

Always remember – if you plan a workload for 70% utilization numbers you are already at the ceiling



I/Os per second –vs- MBs per second

These are natural enemies!

You can do more I/Os if each one is small

You can move more data if each I/O is big



Important performance stuff that doesn’t matter

Read / Write ratio

Cache hit ratio

Okay – I lied. It does matter but you can’t do anything about it!



Raid protection choices

Raid-1 – far less than in the past

Raid-5 – far more than in the past Split about 50/50 between 3+1 and 7+1 Performance is usually equal – choose based on rebuild time

Raid-6 – becoming very popular for large capacity drives Much less often on smaller drives Watch the performance of the DA processors

As of 5772 code you can intermix all Raid types in one array

Flash Drives only support Raid-5



It’s time to embrace tiering

There are lots of ways to do tiering

Drive speed appears to be the best choice

Then pick the drive capacities necessary to support the expected workload

Virtual LUN Migrator Included with Symmetrix Optimizer as of 5772 code Moves LUNs within an array Target can be equal or larger Raid protection can be changed during the migration (5773 code) Non-disruptive Groups of moves can be defined Did I mention that the move is non-disruptive?

What to move where?



Flash Drivetargets?

SATA IItargets?

2



Pay attention to Virtual Provisioning

Virtual Provisioning (Thin Provisioning) arrived in 5773 code

EMC did it right

In almost all of the customer environments EMC tested the results were the same

Virtual Provisioning wins in performance This is the ultimate way to spread your data “wide” VP is much easier to manage VP is must faster to provision VP is much better at capacity utilization VP lets you allocate whatever amount you want.



You have to monitor a Symmetrix

The problem is kind of strange

A Symmetrix is powerful enough to hide your sins…

… until it reaches some limit and then you’ve got a problem!

Let WLA publish to an internal website – but don’t publish too much

Set thresholds to deliver the message clearly



Use Optimizer to keep the disk utilization balanced

As arrays get larger and larger Optimizer becomes more important

As disk drives become larger and larger disk seeking becomes a bigger problem

Monitor “seek distance per second”

Moving the heads is honest work for a disk drive but it isn’t very productive


Performance Aspects – from the Server

Make your servers happy

Use channel load balancing software – always!

Please…. Watch your Queue Depth settings

HBA driver defaults of “8” just aren’t large enough

If you are using an eight-way metavolume from a server with two HBAs that can see the meta, then the correct setting is 32.

The formula:

8 * n / h = Queue Depth setting

where n = number of members in the biggest metavolumewhere h = number of HBAs that can see the metavolume

1 © copyright 2008 emc corporation. all rights reserved. symmetrix capacity planning and...

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