gjournal: what is it good for?

[Andrew Reilly]

Hi David,

On Wed, Apr 21, 2010 at 12:20:46PM +1000, David N wrote:
> Gjournal on my systems are pretty quick on startup after a power outtage.

Great to hear!

> What kind of disks are you using? Or what hardware are you using?

Several: main /usr is on a gjournal on top of a gmirror over a
pair of Samsung 1TB 3.5" SATA drives, but I have other gjournals
on a 750G WD SATA, a 1.5T Seagate and another 1TB WD MyBook
firewire unit.  There is brokenness in the firewire connection
that results in me always coming up manually through single-user
mode, at the moment.  In single user mode pilot error is
sufficient to account for the problems that I was having with
mount vs fsck of the gjournalled drives, I'm fairly sure.

The firewire issue is strange: at boot-up the fw stack (this
is 9-current) doesn't reset the bus well enough or for long
enough for the drive to be fully recognised and show up in /dev,
but a post-boot "fwcontrol -r" does the job nicely.  It's a bit
inconvenient that fwcontrol is in /usr/sbin, rather than /sbin,
so it's not available until the rest of the mounts are complete.
USB "works" but is sufficiently slower that I'm prepared to
hand-hold the boot process in order to have my backups finish in
reasonable time.

> Might be the disks are ignoring the BIO_FLUSH.

Not sure: how could I tell?

Thanks for the support and suggestions.

Cheers,

-- 
Andrew