Thursday, July 19, 2012

EMC VNX Storage Pool Design & Configuration

The EMC Whitepaper on VNX Best Practices h8268_VNX_Block_best_practices.pdf is the way to go, I used version 31.5 as it is the most current one available.

Storage Pools vs Raid Groups vs MetaLuns

From an design perspective, MetaLuns were basically replaced by Storage Pools, Storage pools allow for the large stripping across many drives that MetaLuns offers, but with a lot less complexity. MetaLuns are now generally used to combined/expand a traditional LUN.  Raid Groups have a maximum size of 16 disks, so for larger strips this isn’t a viable option.  For situations where guaranteed performance isn’t critical, go with Storage Pools, use Raid Groups if you need deterministic (guaranteed) performance.  The reason behind this is that you are probably going to create multiple LUNs out of your storage pool, so this could lead to one busy LUN affecting the others.

Raid Level Selection

Assuming your going with a Storage Pool, your options are Raid 5, 6, or 1/0.  If you are using large drives (over 1TB) then Raid 5 is not a good choices because of long rebuild times, Raid 6 is almost certainly the way to go.  Always use suggested drive numbers in the pools, Raid 5 is 5 disks, or a number that evenly divides by 5, Raid 6 & Raid 1/0 is 8 disks or a number that evenly divides by 8.  If you use less than the recommended you will be wasting space.

How Big of a Storage Pool do I start with?

Create a homogeneous storage pool with the largest number of practical drives.  Pools are designed for ease-of-use.  The pool dialog algorithmically implements many Best Practices.  It is better to start with a large pool, as you add disks to the pool, it does not (currently) restripe the disks, and therefore if you only added 5 disks to an existing 50 disk pool, the new LUNS would have much lower performance.   The smallest practical pool is 20 drives (four R5 raid groups).  It is recommended practice to segregate the storage system’s pool-based LUNs into two or more pools when availability or performance may benefit from separation. 

I am only covering a small portion of what you need to know.

When dealing with storage, there are thousands of options, homogeneous drives vs. heterogeneous, Thick vs. Thin Provisioning, Fast VP Pools, Drive Speeds, Fast Cache and Flash Drives, Storage Tiering, the whitepaper above does a great of of detailing all of that, I won’t try to improve on what EMC has said.


Jonathan Garrett said...

HI Brian

Another VNX doc that I found because the link doesnt seem to work is here:

thanks for you blog.

Brian Smith said...

Thanks Jonathan, that looks like good stuff.

neeru v said...

Hi Brian,

I need one help from you. Can you explain RAID 5 ( 4+1 ) and RAID 5( 8+1 ). I have read this in an EMC storage product. They have mentioned this kind of configuration for RAID 5. can you tell what they are actually trying to to do with this configuration ?

Larry said...

RAID 5 (4+1) simple means a RAID 5 set consisting of 5 disks, it is referred to as 4+1 as you loose the capacity of one disk for parity.
Same applied to 8+1, it is just a RAID 5 set consisting of 9 disks, but you can only use the capacity of 8 of those disks as you loose one to parity.

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