From: gezelter@rlgsc.com
Newsgroups: comp.os.vms
Subject: Re: Volume Sets
Date: 6 Nov 92 16:07:42 GMT
Organization: Robert Gezelter Software Consultant, Flushing, NY

In article <9211051918.AA09504@ucbvax.Berkeley.EDU>, SYSTEM_JM@UNODE2.NSWC.NAVY.MIL ("SYSTEM SUPPORT") writes:
> Date sent:  5-NOV-1992 14:01:03 
>>Nigel - We have several volume sets here, and they've worked just fine
>>for us.  One is two 1.1-gb RA90s, another is three RA90s, and the other
>>is four 1.5-gb RA92s.  One of them has tens of thousands of All-In-1
>>files on it.  They're not as efficient as stripe sets, but they don't
>>cost extra money either.  And, as you say, each set fits on a single
>>DAT tape (using data compression).
> 
> Have you *ever* had a disk in your bound volume set go bad?!  The bad news
> is that instead of restoring one disk from your tape backups, you'll have to 
> restore the *entire* volume set.  When it work, it works good.  Gee, how many
> tapes will it take to restore the four 1.5GB volume set?! And how much time?!
> *******************************************************************************
> ** Jim Matthews                                                              **
> ** Naval Surface Warfare Center Dahlgren Division                            **
> ** Code N23A                                                                 **
> ** Dahlgren, VA 22448-5000                                                   **
> ** Internet: system_jm@unode2.nswc.navy.mil                                  **
> *******************************************************************************
> 
> 
-- 
Jim,
 
Actually there is a quite good solution to the backup of large 
volume sets. If you manage your users by department, project, or 
some other designator, then you can have the best of both worlds. 
The advantages of a volume set for disk space management, and 
backup tapes that do not span many tape volumes. 
 
They key is running your backups on a department by department 
basis, rather than a volume by volume basis.  For example, 
consider a volume set consisting of disks DUA1, DUA2, and DUA3.
Doing the backups on a volume basis would require a tape save set 
equal in size to the sum of all the volumes.
 
However, in reality, the volume set contains the following 
directory trees (defined at concealed, rooted logicals): 
 
          DISK$USERS
          DISK$ALLINONE_ADMIN
          DISK$ALLINONE_ACCTNG
          DISK$ALLINONE_ENGNR
          DISK$ALLINONE_CUSTSUPP
          DISK$NEWS
          DISK$PRODUCTION
          DISK$PRODUCTION_DATA
 
The backup procedure that I recommend in such a configuration is 
to back up each of the directory trees as if it were a seperate 
disk. Thus, each of the backups is guaranteed to be of manageable 
size. Additionally, this permits different backup rules for 
different groups (some groups every day full backup, some 
incrementals, some groups every two days, etc.).
 
I hope that this is helpful. If I have been unclear, or if I can 
be of further assistance, please feel free to give me a call or 
send me an Email.
 
- Bob
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