Since the answers I have seen so far, tend to vote against collocation,
let me contribute my opinion. I recently enabled collocation in one of
our storage pools when I saw the increasing number of tapes in it. With
collocation turned off, many of these volumes have to be mounted when
restoring a disk. With collocation enabled (and after some time, since,
as stated by Francis Dequenne, the non-collocated data remains
non-collocated until it is moved somehow), only few tapes have to be
mounted. This makes a big difference, especially for a customer, who
in that situation probably already is highly stressed.

Of course, the price has to be paid during backup. Having a large disk
pool in front of the tape pool helps to keep it low.

Mark Linehan writes:
 > Big question, I finally got reclamation working on our system. It's amazing
 > how many tapes change from full to filling when you change reclamation from
 > 60 to 30! Well, now that this is behind me, the next question I would like
 > to throw out is "How usefull is collocation?" Should I enable it? Will it
 > save me that much time on retores? How much longer will it take to perform
 > backups with collocation enabled?? I have to A S S U M E it is going to
 > take a long time for collocation to first take place when it is enabled.
 >
 > Mark
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Reinhard Mersch                     Westfaelische Wilhelms-Universitaet
Reinhard Mersch                     Westfaelische Wilhelms-Universitaet
Universitaetsrechenzentrum, Einsteinstrasse 60, 48149 Muenster, Germany
E-Mail: mersch AT uni-muenster DOT de                  Phone: +49(251)83-31583