[Xen-users] SAN / LVM backend and partitions

["Reinhard Brandstaedter" <Reinhard.Brandstaedter@xxxxxx>]

Hi,

I'm playing around with Xen using LVM2 based on a SAN storage for VBDs.
Unfortunately I'm not very familiar with LVM2 but so far I get DomUs up
and running with using a logical volume as disk.

What confuses me a bit is the two different ways how to use a logical
volume.
>From the XEN User Manual I see this procedure:
- create logical volume
- create filesystem on LV
- copy system files (the LV is mountable in dom0)

Basically if you want multiple disks (or partitions for /usr,/var, ...)
in the DomU you specify them in the vm config file and need to have
multiple logical volumes on the Dom0 for that, like:
/dev/vg0/vm-root
/dev/vg0/vm-var
/dev/vg0/vm-usr

However I can also only specify only one logical volume in the config
file and do the partitioning in the DomU then. (e.g. if I use
virt-install on RedHat). So the one logical volume would get a partition
table?
Calling fdisk on this volume would print something like that:
# fdisk -l /dev/vg0/vm-root

Disk /dev/vg/vm-root: 6442 MB, 6442450944 bytes
255 heads, 63 sectors/track, 783 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device             Boot  Start  End  Blocks    Id  System
/dev/vg0/vm-root1  *     1      13   104391    83  Linux
/dev/vg0/vm-root2        14     78   522112+   82  Linux swap
/dev/vg0/vm-root3        79     783  5662912+  83  Linux

Maybe this is much more a LVM issue, but which way is the better one for
use with Xen?
If I use partitions in a logical volume can they be mounted in the Dom0
system as well? (e.g. for changing files while DomU is not running)
Are there any considerations for these two aproaches when using
live-migration?

Thanks,
Reinhard


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