Re: What do you use?
From: Scott Mitchell (scott+freebsd_at_tuatara.fishballoon.org)
Date: 01/02/04
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Date: Thu, 1 Jan 2004 23:39:24 +0000 To: Scott W <wegster@mindcore.net>
On Thu, Jan 01, 2004 at 05:59:18PM -0500, Scott W wrote:
> Scott Mitchell wrote:
> >
> >There no particular reason for an ATA RAID to be slower than SCSI, assuming
> >similar disks in each. 10krpm 'server class' ATA disks are available these
> >days, although I don't know that anyone has done a 15krpm one yet.
> >
>
> Does SATA have tagged queing? (I don't know offhand if it does...?)
No idea. I haven't used any SATA stuff yet. Would be surprised if it
didn't though.
> I can guarantee modern SCSI throughput is superior to any of the SATA
> drives I've seen to date. Several of the 'hardware sites' (I think
> Tomshardware did a writeup on this or anadtech among others) agree with
> this statement as well. ATA specs tend to exaggerate their capabilities
> even worse than SCSI specs do- burst speeds are all fine and dandy, but
> not realistic at all in the real world. Meaning basically in short I
> wouldn't choose SATA over SCSI for a production server of any kind where
> speed was an issue. ATA has gotten better by far than it was
> speed-wise, and I'd be OK with it on a personal workstation for any
> purpose, but it's still playing catchup.
Well, I won't disagree with any of that - ATA drives have been aimed at the
consumer market, which wants big & cheap in preference to performance &
reliability. On the other hand, you've got drives like the WD 'Raptor'
that seem to be mechanically what you expect in a server-class SCSI drive,
but with a SATA interface, so the gap isn't that big anymore. I stand by
my statement above though - there's no reason an ATA RAID implementation
_has_ to be slower than SCSI, provided that the disks are up to it. In
practice though, suitable disks are only just now starting to appear.
> Write performance is awful locally, or over NFS? NFS isn't exactly a
> speed demon.
Locally - with RAID-5 you have the extra overhead of calculating the parity
for the block you just wrote, then writing that out to an other drive.
According to the Vinum docs, write performance is ~25% of read, although
how much of that is Vinum and how much is just the nature of RAID-5 I'm not
sure.
> No comment on the unlimited budget as everyone at work just got
> (another) 'mandatory pay reduction'...but I do rememeber and miss those,
> $^#&*(
> ;-)
:-)
Scott
-- =========================================================================== Scott Mitchell | PGP Key ID | "Eagles may soar, but weasels Cambridge, England | 0x54B171B9 | don't get sucked into jet engines" scott at fishballoon.org | 0xAA775B8B | -- Anon _______________________________________________ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "freebsd-questions-unsubscribe@freebsd.org"
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