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Re: [linux-lvm] has anyone used LVM in a HA cluster?

Luca Berra wrote:
On Fri, May 10, 2002 at 07:44:44PM -0500, Steven Lembark wrote:

there is a tool called heartbeat on http://www.linux-ha.org/ have a look at it it really rocks. it already has a resource that supports mounting of partitions on shared media in case an hosts fail, it would be trivial to adapt it for LVM

And make sure the daemons are running in the real time scheduler class.
There exists a state, commomly refered to as "split brain", where the nodes of a cluster "think" the other one is down, which is not the fact. Reason for this may be that the load is so high, that the heartbeat daemon is not scheduled in time to answer the requests (it happened to me with a commercial product). then both nodes mount the filesystem. Usually the inital fsck (or log replay or whatever) is enough to destroy the filesystem beyond repair. But all these things are in no way LVM specific, so it works.

Plan the export and import scenarios (what commands must be executed by the node having the disk mounted and what commands must be executed (vgscan and friends) on the node which mounts a filesystem respectivly) very carefully and take all possible failover scenarios into account, e.g. the active node crashes hard and yu have to scan the volume groups, do the fsck combo on dirty filesystems and mount the volumes.

my experience stems from veritas HA, veritas cluster (which uses a kernel module for heartbeats to work around the scheduler problems) and various versions of veritas volume manager. the volume manager is very similar to a MD/LVM combination.


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