ATA FLUSHCACHE

[Ollivier Robert]

According to Daniel O'Connor:
> Hmm, it is a non fatal error for gjournal, I'm kind of surprised it's a 
> fatal one for ZFS..

It is not a fatal one for ZFS per se.  If I use ZFS in a configuration that
does not require writing on two disks (a gconcat-like configuration), it
works and FLUSHCACHE timeouts are not fatal.

As soon as I try to get it working in a more disk-intensive (raidz in that
case) way, it blows up with a panic.  It seems to point to a flaw in the
ata driver which may not be managing semaphores/mutex correctly or maybe in
the way it uses UMA zones (the panic starts there).

ZFS is only a very reproductible way of triggering the problem.

> If the cache flush really failed (eg due to a stuffed disk) then there 
> really is a problem, but IMO it is likely this is going to be caught by 
> a read or a write operation very soon.

Yes.

> If it is a transient error then panicing seems to be about the worse 
> response :)

Agreed.
-- 
Ollivier ROBERT -=- FreeBSD: The Power to Serve! -=- roberto at keltia.freenix.fr
Darwin sidhe.keltia.net Kernel Version 8.8.2: Thu Sep 28 20:43:26 PDT 2006 i386