USB disk hang - 5.4PRE - gstripe

[John Pettitt]

I just upgraded a box to 5.4PRE and started experiencing regular system
hangs at exactly 1AM - I traced it to BackupPC which was starting it's
run at that time backing up to a gstripe set made from two 300GB USB disks.

The first thing I assumed was that something in Samba or perl didn't
like the 5.4 upgrade so I rebuilt my entire ports tree (portupgrade -fa)
to be sure I had no old libs.  It still fails.

Next I moved the two drives out of their USB housings and put them on
the IDE controller (disconnecting the CD burner to make space).  It's
working fine like that (all be it with disks hanging out the side of the
machine).

So it looks like USB is the culprit.  A few data points:

1) It worked fine on 5.3
2) Motherboard is an Intel D845GVSR with a Celeron D 2.9Ghz and 512Mb Ram
3) USB disk interfaces are from a couple of WD external drives (although
the drives are in fact Maxtor because I upgraded them WD boxes)
4) A single WD250GB disk also on USB seems to work fine  it's only the
stripe set that has a problem
5) When it fails the entire disk system locks (including IDE) but the
machines keeps running until each process locks as it needs to talk to
the disk
6) No meaningful syslog log entries

Any ideas?