Reinhard Brandstaedter wrote:
> 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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> http://lists.xensource.com/xen-users
You have a few basic choices:
1. Export a single LV from dom0 as a full disk, allowing your domU to
see the LV as an entire disk and use partition tables.
2. Export each single LV from dom0 as partitions, allowing your domU to
only see those partitions.
3. Export the VG device from dom0, allowing your domUs to see all LVs.
Since you're using a SAN, you may be aiming to support multiple Xen
boxes on the same device(s). If so, you're probably going to want to
run CLVM. The question is, "Where?" If you use #1 or #2, your dom0s
will have to participate in the cluster. If you use #3, you push the
clustering to the domUs (where I think it belongs.) #3 is less secure,
however.
--
Christopher G. Stach II
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