The MOUNTRetention value is a balancing act, depending upon the current
needs. Here are my notes on it...
MOUNTRetention Operand of 'DEFine DEVclass' and
'UPDate DEVclass' commands, to specify
how long, in minutes (0-9999), to retain
an idle sequential access volume before
dismounting it. Default: 60 (minutes).
The value should be long enough to allow
for re-use of same mounted tape within
a reasonable time, but not so long that
the tape could end up trapped in the
drive upon an operating system shutdown
which does not give ADSM the opportunity
to dismount it. (Always shut ADSM down
cleanly if possible.) Another reason to
keep mount retention fairly short is
that having a tape left in a drive only
delays a mount for a new request, in
that the stale tape must be dismounted
first: this is a big consideration in
restorals, particularly of a large
quantity of data as for a whole file
system, in which case it would be worth
minimizing the MOUNTRetention when such
a job runs. Also, the drive mechanism
stays on while tape is mounted, so adds
wear.
But keep the retention value sufficient
to cover client think time during file
system backups.
Richard Sims, BU
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