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Slow io and high latency on DL180 G5 with 8 SATA drives in RAID5

Slow io and high latency on DL180 G5 with 8 SATA drives in RAID5

I've just invested in a new backupserver, a HP DL180 G5, and I am a bit disapointed with the speed. Again.

The hardware:

System: HP DL180 G5, 2Gb RAM
Controller: P400, BBWC 512Mb
Disk: 8x750Gb SATA in a single RAID5

The system gave me a "slow feeling" so I benchmarked the diskarray with bonnie++.

According to bonnie++ I get about ~65 Mb/s read and ~50 Mb/s write. I consider this slow, especially the read throughput.

The most alarming problem is the latency and CPU usage. When there is IO activity the CPU usage on at least two of the 4 cores reports 100% wait. And the latency on disk block operations is 7843ms according to bonnie++.

The server runs RedHat ES 5.1 and I have compiled a vanilla kernel 2.6.28 with support for xfs and jfs as some people have reported som improvements just by changing fs but it seems not to matter in my case.

I've had almost the same problem before with a DL320S server and it is still not solved. I then just enabled the disk write cache to make the disk perform better but I know it is not a good thing. I tried to enable the disk write cache on the DL180G5 as well but got no significant improvements.

Either the hardware is broken or HP has a problem in the P400 card or the CCISS-driver.

5 REPLIES
KarloChacon
Honored Contributor

Re: Slow io and high latency on DL180 G5 with 8 SATA drives in RAID5

have you tried playing with write and read values???
Didn't your momma teach you to say thanks!

Re: Slow io and high latency on DL180 G5 with 8 SATA drives in RAID5

you mean distributing the cache between read/write. Yes I've tried that and 75% write and 25% read seem to give the most but it didn't fix the problem.
KarloChacon
Honored Contributor

Re: Slow io and high latency on DL180 G5 with 8 SATA drives in RAID5

hey

I don't know if you already tried this:

Enabling "drive write cache"

check the attachment for the steps

Didn't your momma teach you to say thanks!
KarloChacon
Honored Contributor

Re: Slow io and high latency on DL180 G5 with 8 SATA drives in RAID5

sorry forget it
you already did it
Didn't your momma teach you to say thanks!

Re: Slow io and high latency on DL180 G5 with 8 SATA drives in RAID5

Try running iostat. If you want greater reads perhaps a mirrored configuration would be better than raid. 7843 ms is 7.8 seconds. Try Iostat with csvpng or tlviz set see what is going on. Could your applications not be taking advantage of larger block read and writes ?