On Mon, 2009-09-14 at 09:09 +0100, Mark Watts wrote: > On Mon, 2009-09-14 at 09:26 +0200, Florian Haas wrote: > > Using ext3 on top of dual primary DRBD is a sure fire way of destroying > > data. Does that answer your question? > > I have seen (and used) allow-two-primaries with ext3, when using the > drbd block device driver for Xen to allow live migration of a DomU > between two nodes where the DomU is given a full dedicated drbd block > device for its backing store. > > However, for 99.999% of the time DRBD is running in Primary/Secondary > mode and it is Xen which controls promoting and demoting each side as a > migration. Note that I believe Xen is using this in order to prove to > itself that the remote node is capable of accepting disk-writes and is > thus safe to migrate to; it does not, I believe, allow writes to happen > on both nodes at the same time in the general case. > > This is the _only_ case I know of where allow-two-primaries and ext3 can > co-exist, if only for a very short and controlled time. For anything > else Florian is right - kiss goodbye to your data.
Looking back on my notes, I'm totally wrong here. DRBD/Xen live migration does NOT involve ext3. I'm thinking about something entirely different. http://www.drbd.org/users-guide/ch-xen.html ext3 + allow-two-primaries will destroy data. /me goes for coffee. -- Mark Watts BSc RHCE MBCS Senior Systems Engineer, Managed Services Manpower www.QinetiQ.com QinetiQ - Delivering customer-focused solutions GPG Key: http://www.linux-corner.info/mwatts.gpg
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