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Re: [Linux-cluster] Getting started with cLVM

On 10/15/2012 04:41 PM, Eric wrote:
I've been reading about cLVM and I'm having a difficult time getting my mind wrapped around The Big Picture.

Looking at Figure 1.2, “CLVM Overview, of  the Red Hat LVM Administrator Guide I'm a bit puzzled. Specifically: Are storage devices exported directly to cLVM daemons? Or are LV's exported directly to cLVM daemonds for consumption? Or will another shared-disk protocol (e.g., GNBD or iSCSI) be required for "the last mile"?

Eric Pretorious
Truckee, CA

Clustered LVM, fundamentally, swaps out the normal internal locking to DLM (distributed lock manager), which is provided by cman under EL6 and corosync (v2+). Beyond this, you can think of LVM as you always have.

So, commonly, the PV(s) would be some form of shared storage; DRBD and SANs are the most common I think. When you pvcreate /dev/foo (foo being your shared storage), you can immediately 'pvscan' on the other nodes and see the new PV. Likewise, once you assign the PV to a VG on one node, 'vgscan' on all the other nodes will immediately see the new/expanded VG. Likewise with LV creation/resize/removes.

Beyond this, there is nothing further special about clustered LVM over "normal" LVM.



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