Summary: Swap partition vs. Swap file

From: Christoph Baumhof (
Date: Wed Aug 18 1993 - 03:04:12 CDT

This is the summary to my question about swap files. Sorry for
the late response, but I was away from my work for the last three

On Jul 22, I wrote to comp.sys.sun.misc:
: System: Sun IPX, SunOS 4.1.1, 32M RAM
: This machine has a 32M swap partition (sd0b) and a 128MB Swap file.
: The problem: When two processes using 25-40M each are running, the
: system is swapping heavily (I'd say this is perfectly normal), but
: sometimes after a couple of minutes of heavy disk activity the
: system just stops:
: Watchdog Reset
: Window Underflow
: and I'm left at the boot ROM prompt. No kernel messages, no syncing.
: I'm clueless as to what's happened, but it's quite repeatable. Is it
: possible that the swap file causes the problems? Should I repartition
: the disk and add another swap partition? Or am I totally mislead and
: the problem hides somewhere else?
: P.S.: Upgrading to 64M of memory is not an option at the moment.
: P.P.S.: I'm not using TMPFS (just in case this is important)

| Date: 22 Jul 93 15:11:32+0200
| From: Basile STARYNKEVITCH <>
| I'm no longer a SunOS4 user (using only SunOS5), but a few remarks:
| 1. Upgrade at least to SunOS4.1.3. 4.1.1 had some naughty bugs related
| to memory managment
| (maybe including your problem.. i don't know).
| 2. Mixing swap disk & swap file is a bad thing. SunOS seems to put swap on
| both things, and swapping on a file is much slower than on a disk
| (ie a partition). I did it occasionnally, but noticed bad
| performance.
| 3. In my opinion, it should make no difference to swap on 2 different
| partitions (and even swapping on 2 different disk is considered better)
| than to swap on 1 big partition.

ad 2.: I imagined that, but I didn't want to repartition my disk until
        I knew it would work.

| Date: Fri, 23 Jul 1993 09:28:01 -0300
| From: Peter Steele <>
| I'm using swap files heavily on our Sun systems and have never had this
| problem. On one system we have over 400MB of swap file space allocated
| over various drives. We've never had this problem on any of our systems.
| Presently we have 4 Sparc-10's and a Sun-670. All the systems have
| lots of memory as well (96-128MB).

| Date: Tue, 27 Jul 93 16:11:31 CDT
| From: (Tim Ramsey)
| Are you sure that the swap files were created with "mkfile" and not
| "mkfile -n"? The -n option creates a sparse file which has its size
| set to what you indicated but has no space initially allocated. If
| you swap to a sparse file under 4.1.1 you get the behavior you have
| seen.
| See Also: mkfile(1), lseek(2), stat(2) {st_size vs. st_blocks}

I tried the following, all with exactly the same results as described
in my post:
- 32M swap on sd0b, 128M swap file allocated with "mkfile -n"
  (original configuration)
- 32M swap on sd0b, 128M swap on sd1b
- 32M swap on sd0b, 4 swap files of 32M each allocated with "mkfile"
so I think that wasn't the problem.

The solution was this:

| Date: Fri, 23 Jul 93 14:24:41 PDT
| From: (Russ Poffenberger)
| Try looking for the MBUF patch, 100330 I believe.

I installed 100330-06 and it seems that the machine now runs stable.
I only tested the 32M sd0b, 128M sd1b configuration, but I think that
the swap file configurations would run stable too.

Many thanks to all who responded.


Christoph Baumhof                   Institute for Applied Mathematics                      University of Karlsruhe

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