Re: filesystem information

On Mon, Jun 30, 2008 at 12:30:38PM -0400, Jim wrote:
On Mon, Jun 30, 2008 at 7:30 AM, Bill Moran <wmoran@xxxxxxxxxxxxxxxxx> wrote:
In response to Jim <stapleton.41@xxxxxxxxx>:

I have a computer that is in a situation where it is losing power
occasionally. All but one of the filesystems are going along fine.
Once file system seems to lose data on a power outage. Even if it only
reads a file, and doesn't write it, it may still lose a file (ex,
about half the audio files on my xmms playlist, a couple data files in
my wine directory that, to my knowledge, are unlikely to be written
after they are first installed).

What I'd like to do is get an output of the flags and options on my
filesystems to see what is different between that filesystem and the
others. Any suggestion on how to do that? This particular FS has
lasted through several rebuilds since it doesn't hold OS critical
stuff, just data files.

tunefs -p and/or dumpfs -m

Any suggestions?

Sounds like you're on the right track with hunting this down. Perhaps
turn softupdates off and mount the filesystem sync if you're seeing
lots of power outages.

Ans set 'hw.ata.wc="0"' in /boot/loader.conf to stop the drives from
caching writes.

Thanks, it looks like the 'good' filesystems have softupdates off
(except one), and the one the broke has it off. I thought softupdates
were supposed to fix this? Is gjournal a better solution? Is 'just use
neither' a better solution?

WRT softupdates/gjournal, see below.

In case of frequent power outages, I guess the right answer is "get a
UPS". :)

Without a UPS nothing can protect you against power outages. Even when
running the filesystem with the sync flag and setting ATA devices to
write-through the cache cannot guarantee you won't lose data. If the
power fails when a write is in progress, you're screwed.

A proper UPS with monitoring software will give your system time to shut
down properly (finishing writes, unmounting etc) before its battery runs out.

Any reference material on the subject

See http://en.wikipedia.org/wiki/Soft_updates :

Instead of duplicating metadata writes in a journal, soft updates work
by properly ordering the metadata writes to guarantee consistency
after a crash. Like journaling, soft updates do not guarantee that no
data will be lost, but do make sure the filesystem is consistent

In FreeBSD softupdates have a longer track record than journaling.

Roland
--
R.F.Smith http://www.xs4all.nl/~rsmith/
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