[comp.os.vms] Volume sets

nagy%43198.hepnet@LBL.ARPA (04/14/87)

Some points for/against volume sets:

	1. Too many volumes in a volume set is probably hazardous
	   to a system manager's health.  Especially in a software
	   developement or normal timesharing environment where there
	   are lots of little files on the disks...

	2. Free space on members of a volume set are used in parallel
	   by writing a new file on the member with the greatest
	   amount of free space instead of completely filling member
	   #1 then filling member #2, etc.   This has promotes
	   point #3:

	3. Volume sets to improve performance by bring more seek arms
	   to play on the file system.

	4. In my past life as a system manager, I'd only played with
	   dual-disk volume sets: 2 pairs of RA81s and a pair of RM80s
	   as 3 separate volume sets.  No problems beyond the usual.
	   Online backups proceeded as before and did NOT affect the
	   users any more adversely than online backups did before I
	   installed the volume sets.

The "great" argument for volume sets and for making ALL your file system
one giant volume set is make it easy for users to locate the files of
other users since they don't have to remember which disk user X is on.
This argument is actually rather specious under VMS V4.x: the solution
to the "problem" is to define a logical name which is a search list of
all the mounted disk volumes in the public file structures:

	$ define  usr$disks  usr$disk1:,usr$disk2:,usr$disk3:,usr$disk4:

Thus anyone can locate anyone elses file by using the usr$disks logical
name as the "device" specification.  This assumes that a person only has
a single top-level directory on the set of disks listed in usr$disks;
this does not seem to be much of a restriction.

9070NATS@MUCSD.BITNET (Keith Natschke) (02/02/88)

In light of all the discussion about volume sets, I would like to describe
our experience with them. Although I don't recommend them to everybody,
we have had some success increasing RMS throughput by utilizing a volume
set.

We have one volume set consisting of 2 RA81 disk drives dual ported
to 2 HCS50's. The set is shared by 3 different applications, student financial
aid, student fee accounting and library serials. The financial aid and fee
accounting use several large indexed files. We took advantage of the volume
sets by breaking the files into multiple areas, one area for the data and
one for each index. We then placed the data area on one volume and the index
area(s) on the other volume. This resulted in a dramatic decrease in direct
I/O's and connect time when processing these files.

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MM      MM   UU      UU         Keith S. Natschke          Analyst/Programmer
MMM    MMM   UU      UU         Marquette University
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