[Linux-cluster] Getting started with cLVM

[Digimer]

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.

hth

digimer

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