On Tue, Jan 05, 2010 at 11:30:01AM -0800, Stuart D. Gathman wrote: > On Tue, 5 Jan 2010, Madison Kelly wrote: > > > I know that, currently, this isn't supported. Would someone be able to > > explain or point me at a place to read up on what is holding this feature > > back? What are the difficulties? Is it just a question of time, or are there > > certain technical hurdles in the way? > > 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. > > However, you can obtain the same effect using a SAN. Have one > machine run LVM (and raid, etc), and export LVs via AoE or iSCSI. Of > course, that LVM machine now becomes a single point of failure... > > Here's an idea (someone probably already thought of this, but..), > have one machine in a cluster elected "master" for a VG, and have all > reads/writes from other machines go through the master via AoE or > iSCSI. When failure of the "master" is detected, elect another > machine to take over as master. Sort of a rotating SAN server. > Interesting idea. :) Ray _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
