Date: Mon, 16 Nov 1998 10:13:50 -0800 (PST) From: David Wolfskill <dhw@whistle.com> To: hackers@FreeBSD.ORG Subject: Re: dump(8) very slow Message-ID: <199811161813.KAA23880@pau-amma.whistle.com> In-Reply-To: <98Nov16.112411est.40348@border.alcanet.com.au>
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>Date: Mon, 16 Nov 1998 11:24:32 +1100 >From: Peter Jeremy <peter.jeremy@auss2.alcatel.com.au> >I wrote: >>Unfortunately, dump(8) is distinctly sub-optimal as far as reading the >>disk is concerned..... >David Wolfskill <dhw@whistle.com> wrote: >>Well, what I do, in large part to deal with this, is have amanda run >>dump for me. >Amanda definitely addresses the `how to backup a network' problem, but >it doesn't address dump's underlying poor performance. Sort of. The insertion of the hlding disk/speed-matching buffer also permits multiple filesystems to be dumped at the same time. This is a non-trivial win. >I agree that decoupling the disk reading from the tape writing is >beneficial. My problem is that the _average_ disk reading speed is >too slow to keep the tapes streaming. In this environment, memory- >based utilities like team and buffer will (at best) just extend the >time between streaming pauses. Amanda does get around this problem, >but needs enough disk space to cache the entire dump - which I can't >currently afford. With amanda, I'm seeing an average tape-writing speed of about 1280 KB/sec., against a tape drive that has a rated hardware throughput of 1500 KB/sec. -- and this is with the hardware (also) compressing the data. (I need to get a copy of the Quantum docs so I can figure out what SCSI commands to feed the drive to tell it to not bother compressing, since I prefer to do that myself.) >Speeding up dump should also shorten the duration of backups - which >can hardly be bad. True, but being able to do more than one at once is pretty significant. I understand that some folks may not be able to afford the disk space, but the cost of same is becoming less of a hurdle as time passes. Were I to start from scratch, I'd set up a dedicated system for doing backups (& the occasional restore) -- just a fairly plain vanilla box, with some extra room for amanda's logs & databases, and a fast dedicated drive for a holding disk. Of course, the tape drive(s) would be hung off of this box, too. That way, upgrading the box could involve minimal disruption for Real Work. david -- David Wolfskill UNIX System Administrator dhw@whistle.com voice: (650) 577-7158 pager: (650) 371-4621 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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