Re: Very low disk performance Highpoint 1820a
From: Arne (arne_woerner_at_yahoo.com)
Date: 04/28/05
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Date: Thu, 28 Apr 2005 09:08:47 -0700 (PDT) To: Steven Hartland <killing@multiplay.co.uk>, Eric Anderson <anderson@centtech.com>
--- Steven Hartland <killing@multiplay.co.uk> wrote:
> From: "Eric Anderson" <anderson@centtech.com>
> >> Where do I start looking?
> > First, understand that RAID 5 is dependant on fast hardware to
> > performa
> > the XOR operations. A single disk without any RAID can easily
> > outperform a RAID array if the RAID array is on a 'slow'
> > controller.
> > The Highpoint controllers are not exactly high-end fast RAID
> > controllers, so ~50MB/s isn't too bad for that I would say.
> > Did you
> > happen to try a vinum RAID5? How about a stripe?
>
> The quoted benchmarks for this controller are ~500MB/s with 8
> raptor disks. Its a hardware RAID 5 with 8 SATA channels on
> 64Bit PCI-X
> @ 133Mhz so under the current setup it should be achieving
> ~250MB/s
> Im only getting 50MB/s which is just silly.
>
There was a discussion some months ago. It seemed like ata disc
i/o throughput is in R5 abou 50% slower than in R4. I was able to
see that here in my setting, too. But I have to admit, that my
hard discs are probably confused by my experiments with the
write-cache-disable sysctl...
> It was also my inderstanding that the XOR is only done on write
> not read.
>
Yes! The data can be constructed without the parity block, if all
other discs are available. But it might be faster, to use the
parity block in some rare cases (e. g.: the disc that holds parity
data is idle but the others are not AND all corresponding blocks
but one are already in cache memory :-) ).
> > You could make two RAID 5's with the controller, and then
> > stripe those
> > in vinum. You could also do a combo of two stripes in the
> > controller,
> > and a vinum mirror in FreeBSD - that would give you decent
> > performance.
>
> I could but it seems there is something more problematic a foot
> here and would like to investigate the reason for the poor
> performance not workaround it.
>
Did you try RedHat Linux or FreeBSD R4?
-Arne
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