zfs/zpool hang on HEAD and STABLE.

[Joe Holden]

Collective,

I have a fileserver running a zpool of approx. 5TB using mirrored pairs:-

While running HEAD sources from May 22nd or so, all was well, however 
either HEAD or STABLE sources since then cause a non-responsive userland 
(login/csh stops responding, ssh et al, however the kernel is still 
running as I can switch vty's).

Running 8.0-R allows zpool [status] to return the correct info however...

Even with WITNESS and INVARIANTS compiled in, no debug is presented, the 
machine simply stops responding as above.

Machine:
1.8Ghz Celeron 430
3GB ram,
4 * 2TB, 2 * 1TB disks in zpool, 2 * 250GB disks in gmirror for OS.
amd64 branch

I am running with a GENERIC kernel and no custom sysctl/kernel settings.

Does anyone have any suggests as to what I can do to diagnose/debug this 
issue, or has anyone seen similar?

Thanks,
Joe