Performance impact of LVM Stripes

[Stony_3]

How much performance improvement will I gain if I stripe my LV's across a large number of PV's.
What should be the ideal number for stripping.

[Mridul Shrivastava]

That depends on how we are striping:
1. Two disks connected to the same HBA.
2. Two disks connected to different HBA.

Definitely the performance in the 2nd scenario would be more, however you can get better performance in 1st as well.

Moreover a Vg supports max PV 16 so this is the maximum value....

I don't think there is nothing like ideal value it all depends on the database size and your requirement.

[Stony_3]

Mridul, Thanks for your quick response.

What I ment to ask was if one LV extends to large number of disks, what should be the extent of disk stripping(two way / three way/ many way).

What is the difference in performance between say a two way striping and a many way stripping.

Can you point me to some documentation which talks about performance impact by stripping.

Thanks in advance.

[John Guster]

MAX PV is 255, the default is 16.

Anyway, striping across as many disks as possible to get the best performance. striping size has to be decided depending on the application, either oracle, sybase...etc data size may be different, ask application owner what is the size of the data; If your disks are alread in RAID5 configuraton, not too much performance you will get by striping at LVM level.
search docs at http://docs.hp.com
Cheers.

[A. Clay Stephenson · Accepted solution]

There are so many variables that the only reliable answer is to test it yourself. For example, if the PV's are housed in a modern cache-centric array then the benefits of stripping (from the perspective of host-based stripping) may be all but zero. For arrays, it never hurts to stripe across as many PV as you have separate SCSI bus paths for to the array but the gains may be minimal. If the PV's are housed in physical disks (e.g. JBOD's) then the benefits will be real. My experience with LVM LVOL stripping to conventional disks is that above 3 the gains are very marginal because by the time disk 3 has transferred data (probablt to/from its onboard cache), disk 1 is now ready to handle more data.

[Sandman!]

It depends on the target disk system you are using. As already mentioned if you are using one of the high-end storage arrays like the XP512 etc. then the LUNs are already striped (hardware striping) on the storage side. Adding LVM based striping (software striping) to this scenario increases overhead owing to the extra layer of (software-based) striping which usually tends to run slower than the storage side (hardware-based) striping.

On the other hand JBOD (just a bunch of diks) would benefit from LVM based striping. Since they do not have the capability to do storage side striping your only option is to do software striping using a volume manager like LVM.

~hope it helps

[Stony_3]

Thank you all for your responses.
The details as mentioned by
A. Clay Stephenson
&
Sandman
were absolutly spot on. Both the responses deserve a 10 each.

Thank you again and Happy New Year wishes to all.

[Stony_3]

Clear comments on how much performance improvement one gets with stripping