Scott Marlowe schrieb:
On Tue, Dec 9, 2008 at 5:17 AM, Mario Weilguni <mweilguni@xxxxxxxx> wrote:
Alan Hodgson schrieb:
Mario Weilguni <mweilguni@xxxxxxxx> 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.
A customer of us uses the P400 on a different machine, 8 SAS drives
(Raid 5 as well), and the performance is very, very good. So we thought
it's a good choice. Maybe the SATA drives are the root of this problem?
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