On Tue, Dec 9, 2008 at 5:17 AM, Mario Weilguni <mweilguni@sime.com> wrote:
> Alan Hodgson schrieb:
>>>>>>
>>>>>> Mario Weilguni <mweilguni@sime.com> wrote:
>>>>>>
>>>>
>>>> strange values. An individual drive is capable of delivering 91
>>>> MB/sec
>>>> sequential read performance, and we get values ~102MB/sec out of a
>>>> 8-drive RAID5, seems to be ridiculous slow.
>>
>>
>> What command are you using to test the reads?
>>
>> Some recommendations to try:
>>
>> 1) /sbin/blockdev --setra 2048 device (where device is the partition or
>> LVM volume)
>>
>> 2) Use XFS, and make sure your stripe settings match the RAID.
>>
>> Having said that, 102MB/sec sounds really low for any modern controller
>> with 8 drives, regardless of tuning or filesystem choice.
>>
>>
>
> First, thanks alot for this and all the other answers.
>
> I measured the raw device performance:
> dd if=/dev/cciss/c0d0 bs=64k count=100000 of=/dev/null
>
> I get poor performance when all 8 drives are configured as one, large
> RAID-5, and slightly poorer performance when configured as JBOD. In
> production, we use XFS as FS, but I doubt this has anything to do with FS
> tuning.
Yeah, having just trawled the pgsql-performance archives, there are
plenty of instances of people having terrible performance from HP
smart array controllers before the P800. Is it possible for you to
trade up to a better RAID controller? Whichever salesman sold you the
P400 should take one for the team and make this right for you.