4.0 system wedge, scsipi_xfer pool exhaustion?

[Havard Eidnes <he%NetBSD.org@localhost>]

Hi,

a system we have in operation locally was recently upgraded from
netbsd-3 to netbsd-4 (4.0_STABLE).  After this upgrade it has now
wedged twice, usually at times of relatively high disk I/O
activity.  The last time it wedged, I found this in the console
log:

raid1: IO failed after 5 retries.
raid1: IO failed after 5 retries.
sd3(ahd1:0:3:0): unable to allocate scsipi_xfer

Unfortunately, it was power-cycled before I could take a closer
look.

Now, the scsipi layer appears to be of the opinion that failure
to allocate a scsipi_xfer pool item under PR_NOWAIT is supposed
to be a non-fatal problem.  However, raidframe or the upper-layer
user of raidframe appears to be of the opposite opinion.

Any suggestions for what should be done to make this machine a
little more stable?  Pre-allocate more than a page's worth of
scsipi_xfer items using pool_prime() in scsipi_init()?

Regards,

- Håvard