Tape backup speed FreeBSD v. Linux

Tape backup speed FreeBSD v. Linux

Post by Andreas Kle » Thu, 09 Nov 1995 04:00:00






>|> 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 ;-)

--


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Tape backup speed FreeBSD v. Linux

Post by Andreas Kle » Thu, 09 Nov 1995 04:00:00




Quote:

>    There is a known problem in wt.c driver since old 1.1 days.
>    With an Archive FT-60 (ancient 60Mb streamer) this sympthoms
>    were even worse; but I've seen people running Archive 150Mb
>    (or 120?) streamers pretty nice.

Andrew, he is using a SCSI backup device. So the driver isn't wt.c.
It's in /sys/scsi/st.c ... ok ?! ;-)

        Andreas ///

--


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Tape backup speed FreeBSD v. Linux

Post by Andreas Kle » Thu, 09 Nov 1995 04:00:00




Quote:>You don't need s*kin' SYSV shared mem for this, team(1) does the

 :-)

But let's first see, what backup programs and buffer sizes
was used, as Stefan suggested ... If he has a good scsi components,
then it should be possible to keep backup streaming without such
tools.

        Andreas ///

--


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Tape backup speed FreeBSD v. Linux

Post by J Wuns » Mon, 13 Nov 1995 04:00:00



>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 ;-)

Sorry to oppose you in public instead of private mail first, but:

not confirmed.

I've recently been playing with tape block sizes, and i cannot confirm
your observation.  A block size of 96 k actually resulted in the
driver using only 64 k (since this is the maximum it does support),
but apart from this, everything worked well.

This was with some HP DAT drive (forgot the model #, it's a 2 GB
drive) on an AHA2940.
--
cheers, J"org


Never trust an operating system you don't have sources for. ;-)

 
 
 

1. Tape backup speed FreeBSD v. Linux

In addition to buffer size check to make sure that your firmware compression
is being enabled on FreeBSD.  You might need to set a dip switch to set it
on by default.

If the device is scsi check to see if disconnect is enabled on the
controller by default.

I have a WangDAT 3400DX device on a BT946c/p90 and it screams.  It seems to
be able to sustain about 19-20 mb per minute while the system is also
running a full newsfeed and multi-homed web sites.

I've been very impressed by the 3400DX performance and reliability.

Regards,

Mark Hittinger
Internet Manager
WinNET Communications, Inc.

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