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Re: [Linux-cluster] Cluster with shared storage on low budget



Thomas Sjolshagen wrote:
On Tue, 15 Feb 2011 12:49:38 +0100, Nikola Savic wrote:

This is interesting approach. I understand that DRBD with GFS2 doesn't require LVM between, but it does bring some inflexibility:

    * For each logical volume, one has to setup separate DRBD
    * Cluster wide logical volume resizing not easy
    * No snapshot - this is very important to me for MySQL backups.

What is main reason for you not to use LVM on top of DRBD? Is it just that you didn't require benefits it brings? Or, it makes more problems by your opinion?

Just so you realize; If you intend to use clvm (i.e. lvme in a cluster where you expect to be able to write to the volume from more than one node at/around the same time w/o a full-on failover), you will _not_ have snapshot support. And no, this isn't "not supported" as in "nobody to call if you encounter a problem", it's "not supported" as in "the tools will not let you create a snapshot of the LV".

However, you ought to be able to configure one of the DRBD mirror members as part of a split/mount read-only/merge based equivalent and thus get a similar result, I think.

Indeed, that is right - you can drop a server out of the cluster, stop drbd replication and mount it read-only (lock_nolock) and use that as a "snapshot". The added benefit is that it won't cause massive cluster slow-down through lock-bouncing during the backup.

Gordan


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