Re: scsi vs ide performance on fsync's

Jeremy Hansen
2001-03-07T18:29:07Z

So in the meantime as this gets worked out on a lower level, we've decided
to take the fsync() out of berkeley db for mysql transaction logs and
mount the filesystem -o sync.

Can anyone perhaps tell me why this may be a bad idea?

Thanks
-jeremy

On Tue, 6 Mar 2001, Jeremy Hansen wrote:

>
> Ahh, now we're getting somewhere.
>
> IDE:
>
> jeremy:~# time ./xlog file.out fsync
>
> real 0m33.739s
> user 0m0.010s
> sys 0m0.120s
>
>
> so now this corresponds to the performance we're seeing on SCSI.
>
> So I guess what I'm wondering now is can or should anything be done about
> this on the SCSI side?
>
> Thanks
> -jeremy
>
> On Tue, 6 Mar 2001, Mike Black wrote:
>
> > Write caching is the culprit for the performance diff:
> >
> > On IDE:
> > time xlog /blah.dat fsync
> > 0.000u 0.190s 0:01.72 11.0% 0+0k 0+0io 91pf+0w
> > # hdparm -W 0 /dev/hda
> >
> > /dev/hda:
> > setting drive write-caching to 0 (off)
> > # time xlog /blah.dat fsync
> > 0.000u 0.220s 0:50.60 0.4% 0+0k 0+0io 91pf+0w
> > # hdparm -W 1 /dev/hda
> >
> > /dev/hda:
> > setting drive write-caching to 1 (on)
> > # time xlog /blah.dat fsync
> > 0.010u 0.230s 0:01.88 12.7% 0+0k 0+0io 91pf+0w
> >
> > On my SCSI setup:
> > # time xlog /usr5/blah.dat fsync
> > 0.020u 0.230s 0:30.48 0.8% 0+0k 0+0io 91pf+0w
> >
> >
> > ________________________________________
> > Michael D. Black Principal Engineer
> > mblack@csihq.com 321-676-2923,x203
> > http://www.csihq.com Computer Science Innovations
> > http://www.csihq.com/~mike My home page
> > FAX 321-676-2355
> > ----- Original Message -----
> > From: "Andre Hedrick" <andre@linux-ide.org>
> > To: "Linus Torvalds" <torvalds@transmeta.com>
> > Cc: "Douglas Gilbert" <dougg@torque.net>; <linux-kernel@vger.kernel.org>
> > Sent: Tuesday, March 06, 2001 2:12 AM
> > Subject: Re: scsi vs ide performance on fsync's
> >
> >
> > On Mon, 5 Mar 2001, Linus Torvalds wrote:
> >
> > > Well, it's fairly hard for the kernel to do much about that - it's almost
> > > certainly just IDE doing write buffering on the disk itself. No OS
> > > involved.
> >
> > I am pushing for WC to be defaulted in the off state, but as you know I
> > have a bigger fight than caching on my hands...
> >
> > > I don't know if there is any way to turn of a write buffer on an IDE disk.
> >
> > You want a forced set of commands to kill caching at init?
> >
> > Andre Hedrick
> > Linux ATA Development
> > ASL Kernel Development
> > ----------------------------------------------------------------------------
> > -
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> >
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