ADSM-L

Re: ADSM list question MOUNTRETENTION

2000-05-01 14:03:05
Subject: Re: ADSM list question MOUNTRETENTION
From: Richard Sims <rbs AT BU DOT EDU>
Date: Mon, 1 May 2000 14:03:05 -0400
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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