On Fri, 2008-03-28 at 07:42 -0700, Lombard, David N wrote: > 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. > So, I'm trying to understand what to takeaway from this thread: * I should not use them? * I can use them, but having multiple snapshots introduces a risk that a snap-restore could wipe files completely by potentially putting a deleted file on top of a new file? * I should use them - but not use multiples. * something completely different ;) Our primary goal here is to use snapshots to enable us to backup to tape from the snapshot over FC - and not have to pull a massive amount of data over GbE nfs through our NAT director from one of our cluster nodes to put it on tape. We have thought about a dedicated GbE backup network, but would rather use the 4Gb FC fabric we've got. If anyone can recommend a better way to accomplish that, I would love to hear about how other people are backing up large-ish (1TB) GFS filesystems to tape. Regards, -C -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
