Date: Tue, 20 Nov 2001 14:36:05 +0000 (UTC) From: naddy@mips.inka.de (Christian Weisgerber) To: freebsd-questions@freebsd.org Subject: Re: Slow restores on a DLT4000 Message-ID: <9tdpol$2i67$1@kemoauc.mips.inka.de> References: <20011119150711.A7781@northernbrewer.com>
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Christopher Farley <chris@northernbrewer.com> wrote: > I get fairly good throughput on dumps; about 1.6 megs/second, which > seems similar to 'average' expectations that have been published. > During a dump, the drive does not stream, but runs, stops, rewinds, > runs, stops, rewinds... My thinking is that the tape drive is able to > write to a tape faster than my platters can provide the bits. There are two possible issues here. 1. dump is fairly slow and it may indeed not be fast enough to keep the drive streaming. Try dumping to /dev/null and see what speeds you get there. If dump is too slow, you can use a holding disk (or partition): dump to a file on the holding disk and transfer the archive from there to tape using something like misc/buffer or misc/team. 2. Judging from those 1.6MB/s you have compression enabled. My DLT4000 does not stream when compression is enabled no matter what. There is no bottleneck in my setup to explain this and I have already upgraded the firmware. I suspect that the DLT4000 may simply be incapable of streaming if compression is enabled, due to CPU limitations. > Restoring data off a level 0 dump takes about twice as long as the dump > itself, and it also fails to stream. No surprise. Recreating lots of files is slow, even with softupdates or even async mounts. Again, a holding disk will help. > Also, it takes just as long to retrieve a few files off of a dump as it > does to restore an entire dump. It seems like the drive simply reads the > tape sequentially, and if it sees a file I've marked, it writes > it to the disk. Correct. It should stream during that time, though. -- Christian "naddy" Weisgerber naddy@mips.inka.de To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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