[Linux-cluster] Unformatting a GFS cluster disk

[Lombard, David N]

On Wed, Mar 26, 2008 at 11:34:56AM -0400, chris barry wrote:
> On Wed, 2008-03-26 at 10:41 -0500, Wendy Cheng wrote:
> > DRand at amnesty.org wrote:
> > >
> > >
> > > ......The disk was previously a GFS disk and we reformatted it with 
> > > exactly the same mkfs command both times. Here are more details. We 
> > > are running the cluster on a Netapp SAN device.
> > 
> > Netapp SAN device has embedded snapshot features (and it has been the 
> > main reason of choosing NetApp SAN devices for most of the customers). 
> > It can restore your previous filesystem easily (just few commands away - 
> > go to the console, do a "snap list", find your volume that hosts the lun 
> > used for gfs, then do a "snap restore"). This gfs_edit approach (to 
> > search thru the whole device block by block) is really a brute-force way 
> > to do the restore. Unless you don't have "snap restore" license ?
> 
> Wendy,
> 
> We too are using a NetApp. There was talk amongst out IT group that
> these snaps would not work against a raw lun.
> 
> 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

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