<>I'm using PostgreSQL 7.4.2 (package from backports.org)
on a Debian (woody) box. The machine is IBM eServer 345
with two 2.8 Xeon CPUs, it has 1024MB of RAM and
two 15k RPM SCSI disks running in hardware RAID1, which
is provided by the onboard LSI Logic controller (LSI53C1030).


<>With kernel 2.6.x which I was using earlier,
top showed very high "wa" values (which indicate I/O waiting, AFAIK)

It sounds like you are very much bound by disk I/O. Your iostat output indicates a good amount of I/O going on--I bet an iostat -x /dev/sdX would show very high await times (time in ms before an IO request to the device is serviced).

If your RAID controller has a battery-backed cache, check that you have write-back (as opposed to write-through) enabled. This will cause the controller to report data written only to RAID cache and not yet flushed to disk as sync'd. You can experience large gains in write performance this way.

If write-back is already enabled, or enabling it does not give a large enough performance boost, you may need to buy more disks. In general, if you have the budget for lots of disks, RAID 10 is the best you can do performance-wise; if your budget for disks is limited, RAID 5 is the next best thing. Also, you will get more bang for your buck with a larger number of 10k disks than a smaller number of 15k disks.

Good luck,

Bill Montgomery

---------------------------(end of broadcast)---------------------------
TIP 3: if posting/reading through Usenet, please send an appropriate
     subscribe-nomail command to [EMAIL PROTECTED] so that your
     message can get through to the mailing list cleanly

Reply via email to