From: "Kevin Hui - DCS" <khui@cs.toronto.edu> To: "Greg Lehey" <grog@FreeBSD.org>, "Alfred Perlstein" <bright@mu.org> Cc: <freebsd-questions@freebsd.org> Subject: Re: Experiencing very slow raw write speeds on /dev/ad1 Message-ID: <002601c123a4$0981e140$07010101@mtwx1.on.home.com> References: <20010810025156.N85642@elvis.mu.org> <Pine.GSO.4.21.0108101106250.9706-100000@gardiner.cs> <20010812180014.D48115@wantadilla.lemis.com> <20010812033705.V85642@elvis.mu.org> <20010812183324.F48115@wantadilla.lemis.com>
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As I have described previously, I have ported the rawio program to Linux,
and I did use the Linux /dev/raw when I ran the ported rawio benchmark
program for comparison. ("man raw" in Linux to see how to achieve raw device
access).
-Kevin.
----- Original Message -----
From: "Greg Lehey" <grog@FreeBSD.org>
To: "Alfred Perlstein" <bright@mu.org>
Cc: "Kevin Hui" <khui@cs.toronto.edu>; <freebsd-questions@freebsd.org>
Sent: Sunday, August 12, 2001 5:03 AM
Subject: Re: Experiencing very slow raw write speeds on /dev/ad1
> On Sunday, 12 August 2001 at 3:37:05 -0500, Alfred Perlstein wrote:
> > * Greg Lehey <grog@FreeBSD.org> [010812 03:29] wrote:
> >>
> >> Linux and rawio are not really compatible. In Linux you have no
> >> choice, you must go via buffer cache; this can give you results which
> >> look much better. Also, sequential I/O is not very informative,
> >> especially if you only have one process. It would be much more
> >> interesting to look at random I/O and not change the default rawio
> >> parameters (in particular, let 8 concurrent processes run).
> >
> > I was going to say that (linux cheats because it doesn't really have
> > raw io), but I wasn't sure I was up to date enough.
>
> Well, to be *really* up to date, sct has patches for 2.4, confusingly
> called rawio, which do supply character disk devices to Linux. I
> don't know how to get them, though.
>
> Greg
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