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Pavel A
Asked: 2013-01-29 06:28:44 +0800 CST

LVM in cluster -- need an advice

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I'm trying to configure a 2 node cluster with shared storage, but the configuration is probably little unusual. It is described below:

  1. Both nodes have access to a shared storage that has a number of drives. To cluster nodes they appear as local (SAN type of connection).
  2. Node A is going to use half of those drives to assemble a s/w RAID (let's name it SW_RAID1). On top of this s/w RAID there going to be LVM (say VG-1).
    Same for Node B except for that Node B creates its own s/w RAID (SW-RAID2) using other hard drives than node A.
  3. In case of a failure, the remaining node should take over all resources (both SW-RAID1 and 2 with VG-1 and VG-2 respectively).

The picture below illustrates the setup.

cluster topology

The question is: can I use plain LVM for this kind of setup or do I have to go with clustered LVM?

To my thinking I can use plain LVM because each volume group reseeds on an entity (/dev/md*) that is never going to be available on both nodes at a time (ensured by the cluster as it manages the above s/w RAIDs), so from LVM's perspective it is not even A/P.

Am I right? When answering, please, provide some reasoning if possible. Thanks!

raid

2 Answers

  1. If I'm reading your question right, I think you're looking for DRBD. This will transparently keep the two servers' disks in sync, allowing one to fail over to the other without data loss.

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  2. Theoretically you could, but I wouldn't. Sharing volumes between two servers when you have clean dismounts between handoffs should be fairly safe.

    But what you're doing would not give you a clean dismount. This is why you should be using a clustered filesystem: it's designed to handle a server disappearing without corrupting the filesystem.

    And as long as each server is not accessing the same files at the same time, there should be no effective difference in performance.

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