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From: pcg@compsci.aberystwyth.ac.uk (Piercarlo Grandi)
Newsgroups: comp.sys.sun
Subject: Re: Need recommendations on how to select partitions
Keywords: Miscellaneous
Message-ID: <9559@brazos.Rice.edu>
Date: 1 Jul 90 16:09:49 GMT
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In article <9255@brazos.Rice.edu> hughes@src.honeywell.com (Matthew
Hughes) writes:

   >Peter Steele asks about considerations when partitioning disks.  I've
   >never really understood just why Sun recommends partitioning a disk, but

Partitioning a disk used to be useful because:

1) You could dump separately only whole partitions: this is no longer
   relevant. Instead of using dump(8) use GNU tar to dump, and dump subtrees,
   not partitions, with the frequency more appropriate to each subtree.

2) It was a way to have multiple ilists: hopefully this would put inodes
   nearer the files. Cylinder groups do that now.

3) Separate high turnover subtrees from static ones: This was useful not
   just for dumping them separately (see above), but also to separately
   reload them to unfragment them. No longer necessary.

4) To limit a subtree to a specific amount of space:  this is has always
   been the most inane reason. Now we have quotas, but even without quotas it
   was stupid to use such a hard limit as partition size as a substitute.
   Lots of small, rigid partitions create administrative nightmares.

For one, partitioning a disk keeps you from complete and utter
fragmentation, which saves time when loading programs and files.

This used to be true under V7 and System V, which have a time ordered free
list. Under 4.2 BSD derived systems the problem almost no longer exists.
It can be ignored.

   Sun recommends putting all purchased software packages on partitions
   separate from files that change.  This way when you install a new software
   package all the info is in the same place (no fragmentation), so when you
   run the program, the info is read straight off the disk with no jumps to
   other parts of the disk (kinda).  

This is true under any filesystem organization. If you load files that in
some optimal fashion, they will not be moved and will stay optimally laid
out if not modified.

   My question is, why, when you have two or more hard drives, does Sun
   recommend you put the OS and /usr on sd0?  I have no clue.

The obvious rule is to put filesystems between which heavvy copying occurs
on different drives. Typically root, usr, sources, tmp and spool on one
spindle and user files and swap on the other. The idea is to be able to

1) Avoid arm motions between two regions of the same drive
2) Keep each arm doing something different at different times.

Now, if only we had sadp(1M)....

Piercarlo "Peter" Grandi          | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth       | UUCP: ...!mcsun!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK| INET: pcg@cs.aber.ac.uk