forced fsck (again?)

[Andreas Dilger]

On Jan 24, 2008  07:20 -0500, Bryan Kadzban wrote:
> Damian Menscher wrote:
> > At the risk of adding complexity, what about having the SNAPSIZE be
> > automatically determined?  Most users would have no idea what to set
> > it to, and we should be able to guess some reasonable values.  For
> > example, the fsck time can probably be estimated by looking at the
> > number of inodes, how full the filesystem is, etc.  Alternatively, we
> > could just allocate all available space in the LVM.

Yes, this is what my script does, basically guess at a size (1/500th of
the LV size, limited by the amount of free space in the VG).  It should
be possible to override this in a .conf file, but it should be possible
for the majority of systems to run with the defaults.

> > I also have a newbie question: does the fsck of a snapshot really
> > catch everything that might be wrong with the drive, or are there
> > other failure modes that only a real fsck would catch?
> 
> AFAIK, it catches everything.  The LVM2 snapshot is effectively a copy
> of the FS at the time the snapshot was taken.

Yes, it should catch everything.  The snapshot process forces the filesystem
to flush everything to disk in a consistent manner, as if it were unmounted
cleanly and a full copy of the device was made.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.