Date: 24 Oct 1999 16:26:12 +0200 From: naddy@mips.rhein-neckar.de (Christian Weisgerber) To: freebsd-questions@freebsd.org Subject: Re: Why is restore so much slower than dump? Message-ID: <7uv4u4$13f1$1@bigeye.rhein-neckar.de> References: <Pine.BSI.3.95.991024003743.4652E-100000@gwis.com>
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GWIS - Dan Roberts <ddr@gwis.com> wrote: > I'm using a DDS-3 drive to backup files using rdump between two private > 100Mbit ports on a switched network. Dumps are fairly quick, but now I'm > trying to restore a filesystem and it's going deathly slow. I've had also the opportunity to do a full restore this weekend-- after I lost a good chunk of my SCSI periphery to a faulty power cable that insidiously reversed the 5/12V leads--and I haven't been too happy with the speed either. Part of the blame goes to my old tape drive (250kB/s max), but even that didn't run continuously for part of the restore (probably /usr/src or /usr/ports), so a faster drive wouldn't have been any help there. > It's obvious from the slowly flickering drive activity and nic > card lights that the efficiency of this operation could be greatly > improved. Does anyone know what the problem is, and if there is > anything I can do about it? The problem is pretty obviously directory trees with lots of small files that require a disproportional amount of seeking by the hard disk. dump is a clever construct. It forks into five processes: one to watch the tty, one master, and three slaves that do the actual work in a round-robin fashion, so reading from disk and outputting the data run in parallel. restore is much more straightforward. It's just a single process that alternates between reading from tape and writing to disk. First, make sure that the disk writes aren't any slower than necessary. During the restore, mount the file system to be restored asynchronously or enable soft-updates. If that doesn't suffice, you might want to experiment with external buffering (buffer or team from the ports collection). I haven't tried this with restore yet, but it's a godsend for tar/cpio. -- Christian "naddy" Weisgerber naddy@mips.rhein-neckar.de To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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