Several people wrote to me, with essentially the same type
of request:
>
> > If you have all your disks in MPEXL_SYSTEM_VOLUME_SET, I *strongly*
> > urge that you take this opportunity (if you have to reload), to
> > create one (or more) volume sets and place most of your files on them.
>
> I've seen this recommendation before, and I'd be interested in what
> you consider to be the advantages/disadvantages of using additional
> volume sets.
 
 
Advantages:
   If you lose ldev 1, or any other disk in MPEXL_SYSTEM_VOLUME_SET,
   you don't have to reload the entire system.
 
   If you have a 3000 with an internal ldev 1 (e.g., 917, 918, etc.),
   and you lose your CPU, it's easier to roll in a new 917 / 918 (etc.)
   with an internal ldev 1 (MPEXL_SYSTEM_VOLUME_SET) and get back to
   a running system.
 
   If you have applications and/or deparments / users cleverly spread out
   over, say, three volume sets instead of just MPEXL_SYSTEM_VOLUME_SET,
   then you make it much less likely that all active users will get
   impeded by a transaction manager checkpoint ... since every volume
   set is handled independently of every other volume set.
 
   If you want to test a new operating system, and you've been strict
   about keeping user files out of MPEXL_SYSTEM_VOLUME_SET, you can
   do so much more easily (e.g., borrow a new disk drive, install new
   version of MPE, test, and then reboot with your original ldev 1).
 
Disadvantages:
 
   A database (or serial-write-queue file) on one volume set is *not*
   in any way syncronized to a database (or serial-write-queue file
   on a different volume set).  Thus, a DBXBEGIN / DBDELETE / DBXEND on base#1
   followed by the same thing on base#2 (where the two bases are on
   different volume sets), followed by a system failure, could result
   in the DBDELETE having been done on base#2, but not on base #1 (after
   the system reboots and does XM recovery).
 
   Admin of an environment with volume sets is a little harder.  For example,
   you have to be careful about random NEWGROUP commands, since a command
   like "NEWGROUP FOO" will place FOO only on the MPEXL_SYSTEM_VOLUME_SET,
   and not on your favorite volume set (maybe we should request an
   account attribute, HOMEVS, which would apply to all NEWGROUP commands?).
 
   If you lose one disk of MPEXL_SYSTEM_VOLUME_SET (other than ldev 1),
   you may still be able to boot up and access a few user files that are
   on it.  If you lose one disk of a user volume set, you can't access
   any files on the volume set.
 
SS
 
 
--
Stan Sieler                                          [log in to unmask]