5.4-RELEASE-p4: shutdown hangs after rebuiding gmirror

[Michiel Boland]

Hi. I am running FreeBSD 5.4-RELEASE-p4 on a sun V20Z. It has two seagate 
ST373307LC disks. The disks are mirrored with gmirror:

         Name    Status  Components
mirror/raid1  COMPLETE  da0
                         da1

I unplugged one of the disks, then rebooted to see if it would boot from 
just the one disk. Of course there was no problem there.

I then inserted the other disk back in, followed by

  camcontrol rescan all
  gmirror forget raid1
  gmirror insert raid1 da1

After a while the mirror was OK again. I then rebooted for a second time. 
But the machine would not come up. The last lines printed on the console 
were

Syncing disks, vnodes remaining...1 1 0 1 1 0 0 0 done
No buffers busy after final sync
Uptime: 55m39s
GEOM_MIRROR: Device raid1: provider mirror/raid1 destroyed.
GEOM_MIRROR: Device raid1 destroyed.

So it was stuck somewhere in the shutdown sequence between the gmirror 
destruction and the "Shutting down ACPI" bit. Sending a break to the 
console did not produce a DDB prompt, whereas during normal operation it 
would.

I had to power-cycle to get the boot to work again.

If I leave the disks alone, rebooting does not hang the machine.

This is a bit of a nuisance. Who has any idea where to look to 
troubleshoot this?

Cheers
Michiel