[5113] in linux-scsi channel archive
Re: Problem with Scsi Tapes
daemon@ATHENA.MIT.EDU (Michael Meissner)
Thu Nov 12 16:57:26 1998
Date: Thu, 12 Nov 1998 14:35:25 -0500
From: Michael Meissner <meissner@cygnus.com>
To: Marc SCHAEFER <schaefer@alphanet.ch>, linux-scsi@vger.rutgers.edu
In-Reply-To: <723t14$sfu$1@vulcan.alphanet.ch>; from Marc SCHAEFER on Sun, Nov 08, 1998 at 11:50:12AM +0100
On Sun, Nov 08, 1998 at 11:50:12AM +0100, Marc SCHAEFER wrote:
> BTW: you (the guy) should really not gzip. Maybe look into afio which
> supports *file* compression (and not ARCHIVE compression, which is
> dangerous). With file compression, a single tape error will kill
> a file.
On the other hand, particularly with slow Archive tape drives, afio's
compression sucks rocks (you basically start a process for each individual
file). Also, you don't get as much compression by compressing each individual
file, rather than compressing the tape as a whole. When I was still using the
archive drive for my nightly dumps, it was taking 5 hours by using gzip
(including verification, which you need to do anyway), and it would have taken
6-7 hours using afio's compression. Afio also does not support any form of
CRC, etc. on the tape, and unless you use the -4 option, which produces
incompatible tapes, it can't be used if you have more the 65k files that are
hard linked.
My backup strategy is backup everything that needs to be backed up every night
(none of this incremental business, which increases your exposure to risk) onto
one tape and verifying that tape as part of the dump. If the tape doesn't
verify, I just throw it away. In the morning, I just switch tapes. Obviously,
I am not backing up massive amounts of data (currently 4 gigs before
compression to a WangDAT 3800 with hardware comrpression enabled).
--
Michael Meissner, Cygnus Solutions (Massachusetts office)
4th floor, 955 Massachusetts Avenue, Cambridge, MA 02139, USA
meissner@cygnus.com, 617-354-5416 (office), 617-354-7161 (fax)
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