Re: Why doesn't background fsck work ?

[ ... BG fsck ... ]

> > I haven't got softupdates enabled, but I didn't want to enable it,
> > because I've heard that it isn't 100% reliable and I didn't want to lose
> > data....
> 
> Theer have been no problems with softupdates in regard to data
> integrity in either 5.0 or 5.1 release. I do recall a couple of
> glitches at various times in current, probably prior to 5.0-Release.

If you end up with real disk corruption as a result of power
failure, a BG fsck will potentially not correct it.  The CG
bitmaps that are set that shouldn't be are effectively read-only,
and the snapshot permits you to fsck in the background.

However, this assumes that the only thing that's blown is the CG
bitmap.

If anything else is blowm then it's likely your system will panic
when it tries to use corrupt data in some pointer math or some
other use in the implementation of the FS in the kernel.  At this
point you panic.

Then you reboot.

Then you start BG fsck again.

Then you panic again.

Repeat this until a human intervenes and manually runs a full FG
fsck on the disk before letting it be used, and/or someone adds
a count-down counter to the superblock, and the on disk FS layout
changes yet again and becomes incompatible with older versions of
the kernel and fsck, both, and requires a fsck with a special flag
to "upgrade" the FS.

-- Terry