RES: [Xen-users] SAN + XEN + FC + LVM question(s)

[Bruno Bertechini <bruno.bertechini@xxxxxxxxxxx>]

Just complementing Javier's email, I have tested the "online" resizing
inside domU's. It does not work without reboot or (re)-mount the drive /
partition.

Use LVM inside a domU seems to solve this problem, but you DO need to
consider Javier's statements regarding "inner" and "outer" LVM's.

IF we could find ANY documentation about it, and make sure this nested
logical volume Will work witouht problem, I would say this is the *perfect*
solution.

We have *exactly* same scenario here : 03 hosts (dual Quad-Core cpus, 32Gb
of RAM and EMC drive with several luns).

I am on the SAME research of "Best practices" to use this combination.

I think we find the 02 possibilities to GO. 

1) LVM inside domU (downtime 0)
2) reboot the guest (domU) to "see" the changes (I would prefer this
solution, since I personally don't like the Idea to "add" more LV's instead
of resize them.

Regards

Bruno Bertechini

-----Mensagem original-----
De: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] Em nome de Javier Guerra
Enviada em: segunda-feira, 15 de setembro de 2008 13:16
Para: Wendell Dingus
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Assunto: Re: [Xen-users] SAN + XEN + FC + LVM question(s)

On Mon, Sep 15, 2008 at 11:02 AM, Wendell Dingus <wendell@xxxxxxxxxxxxx>
wrote:
> Are there pitfalls or limitations I've not thought of here though? Is this
> approach a "best practices" or is some other method considered "better"?

AFAICS, you're right and ready to go.

the only thing i don't like too much is using LVM inside DomU's.  in
theory some scanning tools could confuse the LVM metadata inside those
volumes with the 'outer' LVM metadata and wreck the whole thing.  i
don't think it really happens in practice...

if you want to avoid LVM inside DomU's, expanding a DomU drive become
a little harder: you have to expand the LV from Dom0, and then somehow
make that resizing known to the DomU kernel. usually that means (at
least) unmounting the device, or even restarting.  after that, just
resize the FS.

if you can tolerate a few minutes of downtime to resize a DomU,
consider avoiding the 'inner' LVM.  if not, or if you're confident no
CLVM tool would confuse 'inner' and 'outer' LVM's, go with your plan.

-- 
Javier

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