[linux-lvm] creating pv's on LVM's for virtual guests

[Christopher Cox]

My personal experience in doing this worked... until I need to manipulate
some things... then the nested LVM data really made life miserable with the
device mapper, etc... long story short... we decided NOT to create the
nested scenario.  Sure... it's not as nice and flexible, but seem to be a
whole lot safer.

For now, we are using LVM on the hypervisor host and using disks as normal,
partitionable spaces (old style) on the VMs.  I would think the opposite
would also work reasonably well... but again, we felt it was safer doing it
the way we're doing it.

Somebody else feel free to chime in....




From:	allan <allane at spinn.net>
To:	LVM general discussion and development <linux-lvm at redhat.com>
Date:	05/09/2011 04:42 PM
Subject:	Re: [linux-lvm] creating pv's on LVM's for virtual guests
Sent by:	linux-lvm-bounces at redhat.com



Hi Steve,

I've had mixed results doing that very thing. Two servers perform very
differently.
One mach, an HP DL380G6 w/ dual quad core Zeon and 6 146G disks installed
with CentOS 5.5 stock xen, lvm, etc. performs
very well. Another machine intended as a low class server, a desktop quad
core AMD, 4 SATA disks installed with stock
CentOS 5.5 same as first mach, has issues with disk perfomance on every
DomU - writes are 1/10 the rate of Dom0 -- I'm
still troubleshooting it.
I see no problem with using LVM on Dom0, carving it up and offering to DomU
virtuals and the virtuals using LVM for
storage. One thing to avoid: do not duplicate an LVM names within the
entire machine. i.e. installer, when told to use
LVM, will create a vg of a specific name. If this name is not overridden,
and you create multiple DomUs with same
process the VG name will be duplicated (as well as the LV names). Avoid
name duplication.
I hope this helps.

Allan

Steve Shorter wrote:
> Howdy!
>
> 		 I am setting up virtual guests to have a LVM created
> from the host. It would be good to use LVM's in the
> guest also.. for easy volume expansion etc...
>
> ie. I am creating pv's/vg's/lvms on top of LVM's. It *seems* to
> work but some of the userland tools need the option -ff
>
> 		 Does anybody see any issues doing this?
>
> 		 thanx - steve
>
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>
>

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