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From: andreas@knobel.gun.de (Andreas Klemm)
Newsgroups: comp.unix.bsd.freebsd.misc,comp.os.linux.hardware
Subject: Re: Tape backup speed FreeBSD v. Linux
Date: 8 Nov 1995 08:22:01 GMT
Lines: 59
Message-ID: <47ppb9$gj@knobel.gun.de>
References: <1995Oct30.090118.28117@state.systems.sa.gov.au>
<475sp3$736@news.rrz.uni-koeln.de>
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Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:8553 comp.os.linux.hardware:20836
In article <475sp3$736@news.rrz.uni-koeln.de>,
se@MI.Uni-Koeln.DE (Stefan Esser) writes:
>In article <1995Oct30.090118.28117@state.systems.sa.gov.au>, chdemgt@state.systems.sa.gov.au writes:
>|> This is a new Tandberg 1200S TDC4120 QIC-1000 tape drive. Being decoded, that
>|> is a SCSI-2 1.2 GB DC-600 quarter-inch cassette drive. It was bought for a
>|> FreeBSD system but the performance was disappointing. The computer (a
>|> 486DX4/100 with a Seagate SCSI-2 hard disk drive) also has a small Linux
>|> partition which can be booted with the help of a floppy disk. Here are the
>|> data rates on backup:
>|>
>|> Claimed by Tandberg in the spec: 12/18 MB/min
>|> FreeBSD 951020 SNAP: 9.1 MB/min
>|> Linux 1.2.x (forget exactly): 15.4 MB/min
>|>
>|> The something was wrong could be detected at once by ear. On FreeBSD the tape
>|> seems to run forward for 1.5 sec and then back for 1.5 sec. This continues
>|> without intermission during the backup. On Linux the tape seems to run
>|> forwards for long periods of time, very occasionally reversing once.
>
>Well, there is quite some information missing ...
>
>1) SCSI host adapter type
>2) Backupp program used under FreeBSD and under Linux
>3) Block sizes used (the defaults can be different,
> even if the same programs are used.
>
>I can keep my HP1533 DDS-2 DAT streaming easily, and it
>needs to be fed at 500KB/s to 1MB/s depending on file
>contents (compressible or not).
Yes, without that information one compares chicken with eggs ;-)
I made some patches to backup on freebsd, which shows you the
data throughput to tape.
Using a Sun DAT with data compression enabled (actually an Archive
Python), you get - depending on compression rate - results of about
560 KByte/sec with FreeBSD-stable (2.1). This would be 31.64 MB / Min.
So one can see, that the SCSI Tape driver is able to keep the
DAT streaming (which means feed the tape with a constant data
rate, so that it doesn't "stop and go").
I use a P90 with AHA2940/Quantum Grand Prix.
I recommend using dump on FreeBSD with a maximum block size of
32Kbyte. If you use a larger blocksize, restore isn't able to
restore the data. There seems to be something wrong in
/sys/scsi/st.c (?). But it's not as tragic as it sounds, since
one can _do_ fine and _fast_ backups with a blocksize of 32K ;-)
--
andreas@knobel.gun.de /\/\___ Wiechers & Partner Datentechnik GmbH
Andreas Klemm ___/\/\/ - Support Unix - aklemm@wup.de -
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