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From: Frode Nordahl <frode@nordahl.net>
Date: Sat, 11 Sep 2004 16:05:39 +0200
To: =?ISO-8859-1?Q?S=F8ren_Schmidt?= <sos@DeepCore.dk>
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cc: current@freebsd.org
Subject: Re: Promise PDC20267 ATA RAID, poor write performance
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On Sep 11, 2004, at 12:49, S=F8ren Schmidt wrote:
>> Doing simple tests show very poor write performance:
>> (reboot)
>> # dd if=3D/dev/zero of=3Dfill bs=3D1m count=3D2000
>> 2000+0 records in
>> 2000+0 records out
>> 2097152000 bytes transferred in 588.383886 secs (3564258 bytes/sec)
>> (reboot)
>> # dd if=3Dfill of=3D/dev/null bs=3D1m
>> 2000+0 records in
>> 2000+0 records out
>> 2097152000 bytes transferred in 68.492015 secs (30618927 bytes/sec)
>
> The only thing I could think of was if you have WC (write cache)=20
> turned off for some reason which yields this result here:

When you say WC, you mean hw.ata.wc, right? It was enabled.

I tried to disable it, and things actually got faster.

# dd if=3D/dev/zero of=3Dfill bs=3D1m count=3D2000
2000+0 records in
2000+0 records out
2097152000 bytes transferred in 346.250049 secs (6056756 bytes/sec)

Maybe there is some timing issues here somewhere, or just flaky cables=20=

:-/

I'll test with other cables and disks and get back.

atacontrol cap shows that the disk has write cache as well as read=20
ahead enabled, is it possible to tune this using FreeBSD tools?

Mvh,
Frode

> pizzabox# dd if=3D/dev/zero of=3Dfill bs=3D1m count=3D2000
> 2000+0 records in
> 2000+0 records out
> 2097152000 bytes transferred in 428.874993 secs (4889891 bytes/sec)
>
> That looks more like your results, but they are also within what I=20
> would expect when not using WC..
>
>
> -S=F8ren
>