Ross Vandegrift wrote:
On Fri, Jan 13, 2006 at 03:06:54PM +0800, Max Waterman wrote:
One further strangeness is that our best results have been while using a
uni-processor kernel - 2.6.8. We would prefer it if our best results
were with the most recent kernel we have, which is 2.6.15, but no.
Sounds like this is probably a bug. If you have some time to play
around with it, I'd try kernels in between and find out exactly where
the regression happened. The bug will probably be cleaned up quickly
and performance will be back where it should be.
So, any advice on how to obtain best performance (mainly web and mail
server stuff)?
Is 180MB/s-200MB/s a reasonable number for this h/w?
What numbers do other people see on their raid0 h/w?
Any other advice/comments?
My employer usues the 1850 more than the 2850, though we do have a few
in production. My feeling is that 180-200MB/sec is really excellent
throughput.
We're comparing apples to oranges, but it'll at least give you an
idea. The Dell 1850s are sortof our highest class of machine that we
commonly deploy. We have a Supermicro chassis that's exactly like
the 1850 but SATA instead of SCSI. On the low-end, we have various P4
Prescott chassis.
Just yesterday I was testing disk performance on a low-end box. SATA
on a 3Ware controller, RAID1. I was quite pleased to be getting
70-80MB/sec.
So my feeling is that your numbers are fairly close to where they
should be. Faster procs, SCSI, and a better RAID card. However, I'd
also try RAID1 if you're mostly interested in read speed. Remember
that RAID1 lets you balance reads across disks, whereas RAID0 will
require each disk in the array to retrieve the data.
OK, this sounds good.
I still wonder where all the theoretical numbers went though.
The scsi channel should be able to handle 320MB/s, and we should have
enough disks to push that (each disk is 147-320MB/s and we have 4 of
them) - theoretically.
Why does the bandwidth seem to plateau with two disks - adding more into
the raid0 doesn't seem to improve performance at all?
Why do I get better numbers using the file for the while device (is
there a better name for it), rather than for a partition (ie /dev/sdb is
faster than /dev/sdb1 - by a lot)?
Can you explain why raid1 would be faster than raid0? I don't see why
that would be...
Things I have to try from your email so far are :
1) raid1 - s/w and h/w (we don't care much about capacity, so it's ok)
2) raid0 - h/w, with bonnie++ using no partition table
3) kernels in between 2.6.8 and 2.6.15
Max.
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