Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!pasteur!ucbvax!RICHTER.MIT.EDU!krowitz
From: krowitz@RICHTER.MIT.EDU (David Krowitz)
Newsgroups: comp.sys.apollo
Subject: Re: more SR10 questions
Message-ID: <8812051455.AA06261@richter.mit.edu>
Date: 5 Dec 88 14:55:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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The reason that incremental backups with WBAK are so slow is that you wind
up having to touch every file on the disk to check the date/time it was
last modified. Unfortunately, the Apollo file system does not store the
DTM in the directory entry of the file, so WBAK must open each file in
addition to opening and reading the parent directory. 

One way in which backups can be speed up is the method used by Workstations
Solutions' backup product. They start clients on several nodes which all
feed data back to a server which writes the tape. Since the clients run
independently of each other they can process several disks simultaneously
and send the server buffers of data which have already been formatted for
the backup tape. The only drawback to this approach is that you wind up 
with files from multiple disks all interleaved in a single backup file on
the tape rather than in seperate backups. It is easier to retrieve files
from a backup when you know for certain which tape it is on. Incremental
backups, however, are frequently done which several disks all on a single
tape, in which case the method used by Workstation Solutions gives the
same results a whole lot faster.


 -- David Krowitz

krowitz@richter.mit.edu   (18.83.0.109)
krowitz%richter@eddie.mit.edu
krowitz%richter@athena.mit.edu
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