On Tue, 5 Jan 2010, Ray Van Dolson wrote:
> > Setting up the shapshot is just a matter of locking and coordination.
> > However, writes to the origin or snapshot (may) require allocating a
> > cluster, copying the origin data, then writing the origin. All of
> > this coordinated with all the machines using the VG. Apart from some
> > cleven invention, this requires global locking on many writes. This
> > is just too inefficient.
>
> Writeable snapshots I guess would be a challenge. But even read only
> snapshots would be great as it would theoretically make backing up
> large, clustered filesystems simpler.
Even read-only snapshots have to handle writes to the origin. And
anytime any machine writes a new cluster to the origin, all machines need their
cluster maps updated so that reads don't pick up the wrong cluster.
--
Stuart D. Gathman <stuart@bmsi.com>
Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.
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