We reached a fairly good performance on a P400 controller (8 SATA 146GB
2,5" 10k rpm) with raid5 or raid6 Linux software raid: the writing
bandwidth reached about 140 MB/s sustained throughput (the hardware
raid5 gave a sustained 20 MB/s...). With a second, equal controller (16
disks) we reached (raid6 spanning all 16 disks) about 200 MB/s sustained.
The CPU load is negligible. Reading performance is about 20% better.
Best regards and my apologies for my bad English.
GT
P.S.: on a P800, 12 SATA 750GB 3,5" 7200 rpm, the hardware raid5 writing
performance was about 30 MB/s, software raid5 is between 60 and 80 MB/s.
Scott Marlowe ha scritto:
> 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.
>
