[Linux-cluster] Cluster with shared storage on low budget
gordan at bobich.net
Tue Feb 15 12:20:04 UTC 2011
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.
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