Re: [Xen-devel] lvm

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> I've just stumbled into the wonderful world that is lvm.
> At the same time I have just created a new partition for a new domain on my 
> xen server and am therefore having to reboot to re-read the partition table. 
> Do xen domains work under lvm vd's? I'd assume yes and I know this has been 
> asked before but I'd like to know the up-to-date answer before I jump in.

It certainly should work, though I can't say I've tested it. 

The only annoyance I can think of is if you want to export an LVM
volume as a whole-disk to another domain (e.g. to appear as
/dev/sda rather than individual partitions /dev/sda1 etc.).
Within dom0, I'm not sure how you'd be able to get a partition
table onto the volume and then populate the internal partitions
with file systems and files.  I guess you'd really want dom0 to
export the LVM volume back to itself as e.g. /dev/sdb so you
could then mount the individual partitions, but this is currently
supported (perhaps device mapper in 2.6 will give us this for free?)

Using lvm should work fine if you take volume per exported
partition approach. It'll all be transparent to the other domain
anyhow, and has the advantage that you can resize individual
partitions.

It should be possible to use the lvm snapshot feature to do CoW
disks. However, the current behaviour is a bit confusing as new
writes go to the main volume and copies of the replaced data goes
to the log volume. Converting the lvm snapshot module into a CoW
modeule with the more conventional semantics should be pretty
easy (original volume stays read-only, writes go to log volume).

We haven't looked too hard at this yet as I think life will be
easier under device mapper in 2.6.

Ian



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