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From: McGuire_Ed@GRINNELL.MAILNET.UUCP
Newsgroups: mod.computers.vax
Subject: VMS: Backup efficiency
Message-ID: <8607192323.AA18361@ucbvax.Berkeley.EDU>
Date: Wed, 16-Jul-86 13:24:00 EDT
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Posted: Wed Jul 16 13:24:00 1986
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Chris,
I came across an archived note you sent in April '86 regarding BACKUP
efficiency.  In part:

>BACKUP efficiency is sensitive to a number of factors.  Tape block
>size is one of the more important ones; the following suggests the
>largest (and most efficient) blocks for each density:
>           800 bpi             8192 ( 8Kb)        bytes/block (default)
>          1600 bpi            16384 (16Kb)        bytes/block
>          6250 bpi            65024 (63.5Kb)      bytes/block.
>The larger the tape blocks, the fewer I/Os are required, and the
>faster things will happen.  I believe TU80s are streaming drives, so
>it may also help to specify the maximum 5 buffers.  (Note that 5*63.5K
>equals 635 memory pages for buffers alone, so allow a large working
>set.)

I must be missing something.  Why not use the maximum block size
permitted by BACKUP no matter what the density?  Are these architectural
limits imposed by the recording method?

McGuire_Ed%GRINNELL.MAILNET@MULTICS.MIT.EDU (MIT-MULTICS.ARPA)