Striping LV's on EMC

[Maceo Lewis]

Hi,
I have read that it is not recommended to perform striping when creating logical volumes on EMC drives. Is there anyone who has anyone benchmark results or experienced a performance degradation when striping lv's on EMC drives?

Mace

[harry d brown jr]

Are you using Raid-S? If so, striping on top of striping probably won't get you much, other than headaches. Let the EMC box handle the headaches.

[Sridhar Bhaskarla]

The performance can degrade if you use small stripes. Please check with your EMC administrator (they don't recommend usually) before doing striping. If it is RAID-5 your stripe size should not be less than the Hardware stripe size. Starting at a minimum of 512k seems to increase the performance.

Else you can use extent level striping if you want to balance your fiber channel paths.

About benchmarking, it is all dependent on the application and the way in which it interacts with the file systems. I would definitely do a benchmarking on another system with the same application with the following options

-Without striping
-With LVM striping of 256k, 512k, 1024k
-With Extent Level striping with default and custom extent sizes

Verify the one that is giving the maximum throughput.

-Sri

[Maceo Lewis]

Harry,
I have 2 EMC's that are using Mirroring and 1 that is using Raid-S. Thanks for the reply.
Mace

[Alan Riggs]

I just went through an EMC implementation. I do not have comparative benchmarks, but I can tell you what I learned:

1) EMC does not have a coherent recommendation for striping.
2) Oracle has released a new recommendation called SAME (Stripe And Mirror Everything) which has some excellent points--BUT oracle is not 100% forthcoming on the benchmarks they publish to support that recommendation.
3) EMC disagree with oracle about the importance of data location on a physical drive. Because . . .
4) EMC likes to pretend that no physical bottleneck ever occurs and all operations will be done in cache.
5) That will never happen in an OLTP environment, but have a LOT of cache can get you closer. Given real world budget constraints, I don't think we can ignore the physical interface just yet. YMMV, of course.
6) The performance of EMC Raid-S is not that impressive. We decided to go with EMC Raid 1 and LVM striping.
7) EMC buffers physical disk writes at 32 Kb, so we saw no reason to stripe in smaller chunks (though we received recommendations from 8Kb to 512 Mb). We decided to use 64Kb stripes.
8) Remember that any BCVs you associate with a striped data volume will also be striped -- this is important if you need good performance on a BDV for any reason.
9) Remember to be very careful when laying out striped columes across EMC hypers. Double striping a physical spindle is bad, m'kay?

*) The above represent my personal observations and conclusions only. The management accepts no responsibility for the consequences to any fool that listens to me.

[Maceo Lewis]

Thanks for the info. My stripe size is set to 64Kb. Even when EMC is set to RAID-S I don't see a problem with performing striping. In RAID-S logical volumes are not striped across physical volumes. That is the purpose of striping to spread data across multiple disks. So, I would think that if you stripe across multiple hypervolumes that are not on the same physical volume you should experience better performance, especially if the stripe size is set to 64Kb.Thoughts?
Mace

[Sridhar Bhaskarla]

As long as the I/Os are small, it is ok with small stripe sizes. However, having small stripe sizes will cause more seek times on the spindles and hence introduce latency for large I/Os. So, though they (HP,EMC) do not recommend to use striping, having large stripes may gain performance. Extent Level striping may be one option.

-Sri

[Scott Pelletier]

Another thing to consider is how the striping will affect your ability to move data around using LVM commands. Since you can't mirror and stripe at the same time (unless you use extend based striping), if you stripe, you will then not be able to to move data around using lvextend or pvmove. I've run into this several times when needing to move lvols around or when needing to migrate from one storage technology to another. Since I've not heard anything conclusive on the topic of striping with EMC Symms, I always choose not to so I don't loose the data movement features.

Scott

[Tim D Fulford]

Have you looked at the average service times of your current setup?

sar -d 1 10

I'd do this at busy times & quiet & compare.

o avserv<2 probably little performance gain possible. EMC cache is doing well
o avserv>15 there is a possibility you could get more out of your disk. EMC cache could be at/past it's limits.
o 2
Just some thoughts on the subject!

Tim