ufs2 / softupdates / ZFS / disk write cache

[Dan Naumov]

On Mon, Jun 22, 2009 at 3:19 PM, Simun Mikecin<numisemis at yahoo.com> wrote:
> 2) I wouldn't use UFS+SU on [S]ATA disks because your background fsck will
> simetimes give up stating something like "unexpected softupdates
> inconsistency" (unless you had disabled write cache, which you don't really
> want to) and you will have to do a manual foreground fsck yourself.

> The choice should (in my opinion) be: ZFS for amd64, UFS+gjournal for i386.
> Both (ZFS and UFS+gjournal) will not have any recovery penalty if you have
> write cache enabled.

You seem to be thinking the way I am thinking :) My biggest concern is
for the new users coming to FreeBSD, most of whom are going to end up
with having UFS2+SU on their SATA disks, which is not the best
defaults to have. I wonder if people running away screaming from
sysinstall code has anything to do with why gjournal and zfs are not
suggested as an option during the system installation procedure. Is
the general consensus that adding these options to the install will
only happen if/when FreeBSD moves on to a new installer system?

Out of curiosity, how many beers would folks have to chime in for
somebody knowledgeable enough to implement direct support for gjournal
and zfs into sysinstall? :)


> If you have a controller with battery backup cache, you could even run ZFS
> with disabled cache flush (i don't know wheter it can be disabled on
> gjournal), but I'm not sure that you will get any real word performance
> improvement by doing it.

In their own documentation, SUN recommends against disabling cache
flushing in most cases, as the performance gain is going to be very
negligible. However, there is a special case with "smart" SAN devices,
where SUN strongly recommends disabling cache flushes because
otherwise you are going to suffer through serious performance losses.


- Sincerely,
Dan Naumov