From owner-freebsd-questions  Mon May 21  7:25:14 2001
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Date: Mon, 21 May 2001 09:24:54 -0500 (CDT)
From: mark tinguely <tinguely@web.cs.ndsu.NoDak.edu>
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To: nvidican@ipsnetwork.net
Subject: Re: erasing a tape volume, (or possible dump is broken?)
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 Nathan Vidican <nvidican@ipsnetwork.net> types:
> I tried to do another zero level dump this evening, on a tape which I 
> had previously used for a zero level dump. It dumped about 1.8gigs, and 
> then asked for the second tape volume; the drive is a DDS-2 
> (4gig/8compressed) internal Seagate SCSI DAT. I used the command: dump 
> -0au /server; when I do a df, the partition /server has only got about 
> 2.1gigs used (out of a possible 4.3 on a RAID array (mirrored via 
> hardware controller), so I know it shouldn't be a capacioty issue). What 
> I'm not sure of though, does dump over-write what's on a tape, or append 
> to it? If the latter is true this would make sense; but if not then how 
> exactly to I force dump to either overwrite with a new volume on the 
> tape each time, or erase the tape beforehand?

Another possible problem beside Mike's observation that you could be
using the non-rewinding tape device is tape streaming. If the data
is not being fed to the tape device at a fast enough rate the tape drive
may be stopping and you will not get the maximum amount of data stored on
a tape. Lack of streaming significantly reduces the amount you can store
on a tape.

Many times hardware compression is a jumper setting on the back of the
tape drive.

--mark tinguely


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