[76] in Athena_Backup_System
Re: Tape layout
daemon@ATHENA.MIT.EDU (Marc Horowitz)
Thu Feb 9 21:56:53 1995
To: Diane Delgado <delgado@MIT.EDU>
Cc: athena-backup@MIT.EDU, Jonathon Weiss <jweiss@MIT.EDU>
Date: Thu, 09 Feb 1995 21:56:31 EST
From: Marc Horowitz <marc@MIT.EDU>
>> Transarc Tape layout (from what I can tell of the sources)
>> looks like:
>>
>> [details removed]
Transarc backup tapes consist of volumes with the format you describe,
separated by real eof markers. I have used this feature in the past
to navigate around afs backup tapes to extract individual volume files
off of partially corrupt tapes and process them individually. The
exact details of this is black magic, but "mt fsf" did work.
>> From what I remember of Exabyte drives (at least the old ones) the
>> inter-record gap is ridiculously large. Lots of separate tapes files
>> means lots of space lost. We could only fill one of those tapes to
>> about 2/3 theoretical capacity before running out of tape.
This depends on the drive. On the exabyte connected to a dec 3100 in
the sipb office, eof markers are 2mb. On the exabyte connected to a
sun ipx in my office at OV, eof markers are only 96k (both numbers
from fms). Since afs stores an entire volume in each tape "file", the
waste is pretty low.
Marc
