topic Re: P400 SAS controller slow on RH in Operating System - Linux

P400 SAS controller slow on RH

jimss — Fri, 10 Aug 2007 03:35:32 GMT

I've got several DL385G1 & G2s running RH3, RH4, and i'ved noticed its disk performance isn't very good for concurrency under load.

The test i'm doing is: duplicate a gigabyte file & delete it, measuring the time taken. Usually its in the order or 20 seconds. Which is good. The issue i'm seeing is, while this is occuring, doing anything else on the machine that requires any disk IO grinds to a halt (until the write has finished). Like if i open a file in VI.

I'm assuming this has something to do with the P400 caching the write, in a FIFO buffer, resulting in the read request from VI to be delayed several seconds (sometimes 10 seconds).

I'm hoping there is a method to optimize the p400 cache/buffer a little better. Or let linux do the buffer/caching itself, (which I assume is why i don't see this on a standard PC IDE/SATA controller).

The disks in question is a RAID 1 mirrored disk. I'm fully up2date with firmware (controller & disks) and drivers (redhat).

Any suggestions would be much appreciated, cheers James

Re: P400 SAS controller slow on RH

TY 007 — Fri, 10 Aug 2007 03:57:24 GMT

Hello,

Does the DL385G1 & G2s include a battery-backed write cache (BBWC) on the P400 controller?

For models that do not include the BBWC, it is available as an option.

The BBWC buffers disk writes so that disk I/O can be handled efficiently.

Thanks

Re: P400 SAS controller slow on RH

jimss — Mon, 13 Aug 2007 01:34:07 GMT

No they don't have battery backed p400 controllers.

The problem I'm seeing is laggy (for want of a better word) performance while copying a single file with no other I/O occuring. On other servers I don't see this, and they standard controllers..

Do you know of a way to disable to controllers cache, to see if this is the cause of the problem?

Re: P400 SAS controller slow on RH

fschicker — Wed, 11 Jun 2008 14:39:27 GMT

hi,

could you solve the problem?

thank you

Re: P400 SAS controller slow on RH

Jon Gomersall — Thu, 12 Jun 2008 10:12:24 GMT

Check out this Forum question

http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=1225006