[74] in Athena_Backup_System
Re: Tape layout
daemon@ATHENA.MIT.EDU (Diane Delgado)
Thu Feb 9 10:49:05 1995
To: Jonathon Weiss <jweiss@MIT.EDU>
In-Reply-To: Your message of "Wed, 08 Feb 1995 20:16:30 EST."
<199502090116.UAA10189@the-other-woman.MIT.EDU>
Cc: athena-backup@MIT.EDU
Date: Thu, 09 Feb 1995 10:48:38 EST
From: Diane Delgado <delgado@MIT.EDU>
Transarc Tape layout (from what I can tell of the sources)
looks like:
<file begin mark>
<volume header>
<volume data>
<volume trailer>
<file end mark>
The <file end mark> and <file begin mark> are not real hardware
device generated eof markers; they are generated by the AFS
backup system software. They consist of some bytes with a
magic number in them. The code does not say why they do this
instead of using the device eof markers.
We might want to consider using real eof markers, since some
devices support ioctls which will allow the software to request
skipping to the next eof marker. For restores, we could then
skip forward n files and start a restore from a volume in
the middle of a tape. I guess you would have to play around
with this to ensure that it's supported on all the tape devices
which we will be using :-).
