How to configure additional swap space?

[Bill Wyatt]

> I believe what happens is unlike some other versions of BSD Unix, when
> you configure more than one swap devices in the conf file, the Ultrix
> kernel turns on swap on those devices when the kernel boots, and doesn't
> wait for swapon.

Unless it's changed recently (I haven't checked since the 3.x upgrade),
the answer is no, the kernel doesn't use additional swap space until
swapon is called (it does use disk 0). We have a uVax with *lots* of 
disks & partitions, and discovered we couldn't automatically boot 
after a crash because `fsck -p' ran out of core when checking several
filesystems in parallel (about 8). We changed fstab to limit fsck to
about 4 or 5 and it's ok, but of course slower. 

> What leads me to this conclusion is we had an 3.0 kernel compiled on
> a system with two disks and we swapped on both of them.  When we copied
> the same system with only one disk, the kernel complained something about
> "can't open device (9,1), retrying...." and I guess it timed out after
> a while.  This was before it started /etc/init.

Some people said that the kernel will hang if you configure a swap
partition that isn't there. If this was true in 3.0 (we upgraded from
2.2 to 3.1 directly), it isn't in 3.1. We get messages such as the
above, but the kernel gives up after one retry (~10 sec.) and
continues booting normally.

Bill Wyatt, Smithsonian Astrophysical Observatory  (Cambridge, MA, USA)
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-- 
Bill Wyatt, Smithsonian Astrophysical Observatory  (Cambridge, MA, USA)
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