[Linux-cluster] Unformatting a GFS cluster disk

[Lombard, David N]

On Thu, Mar 27, 2008 at 03:26:55PM -0400, christopher barry wrote:
> On Wed, 2008-03-26 at 13:58 -0700, Lombard, David N wrote:
> ...
> > > Can you point me at any docs that describe how best to implement snaps
> > > against a gfs lun?
> > 
> > FYI, the NetApp "snapshot" capability is a result of their "WAFL" filesystem
> > <http://www.google.com/search?q=netapp+wafl>.  Basically, they use a
> > copy-on-write mechanism that naturally maintains older versions of disk blocks.
> > 
> > A fun feature is that the multiple snapshots of a file have the identical
> > inode value
> > 
> 
> fun as in 'May you live to see interesting times' kinda fun? Or really
> fun?

The former.  POSIX says that two files with the identical st_dev and
st_ino must be the *identical* file, e.g., hard links.  On a snapshot,
they could be two *versions* of a file with completely different
contents.  Google suggests that this contradiction also exists
elsewhere, such as with the virtual FS provided by ClearCase's VOB.

-- 
David N. Lombard, Intel, Irvine, CA
I do not speak for Intel Corporation; all comments are strictly my own.