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Re: [linux-lvm] [PATCH 10/10] man: document --node option to lvchange



Dne 19.3.2013 18:36, Vladislav Bogdanov napsal(a):
19.03.2013 20:16, David Teigland wrote:
On Tue, Mar 19, 2013 at 07:52:14PM +0300, Vladislav Bogdanov wrote:
And, do you have any estimations, how long may it take to have you ideas
ready for production use?

It'll be quite a while (and the new locking scheme I'm working on will not
include remote command execution.)

Also, as you're not satisfied with this implementation, what alternative
way do you see? (calling ssh from libvirt or LVM API is not a good idea
at all I think)

Apart from using ovirt/rhev, I'd try one of the following behind the
libvirt locking api: sanlock, dlm, file locks on nfs, file locks on gfs2.

Unfortunately none of these solve the main thing I need: Allow LVM
snapshots without breaking live VM migration :(

Cluster-wide snapshots (with shared lock) would solve this, but I do not
expect to see this implemented soon.


Before I'll go any deeper with reviewing patches myself - I'd like to
make myself clean about this 'snapshot' issue.

(BTW there is already one thing which will surely not pass - it's the 'node' option for lvm command - this would have to be made diferently).

But back to snapshots -

What would be the point of having (old, non thinp) snapshots active at the same time on more then 1 node ?

That would simply not work - since you would have to ensure that noone will write to snapshot & origin on either of those nodes?

Is your code doing some transition which needs active device on both nodes
treating them in read-only way ?

Since metadata for snapshot are only parsed during first activation of snapshot, there is no way, the second node could resync if you would have written to the snapshot/origin on the first node.

So could you please describe in more details how it's supposed to work?


Zdenek






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