RE: [Xen-users] Re: DomU on LVM

["Ross S. W. Walker" <rwalker@xxxxxxxxxxxxx>]

Tomasz Nowak wrote:
> 
> Wolfgang Rosenauer <wolfgang.rosenauer@xxxxxxxxxx> wrote:
> >
> > So my plan was to use LVs directly as partitions in the guest
> > /dev/vg/lv1 -> /dev/hda1
> > /dev/vg/lv2 -> /dev/hda2 (or /dev/hdb1 FWIW)
> 
> AFAIK this way is not to be supported in the future.
> I've managed to make it work (for each disk but /root (or /boot))
> but then I've realised there are no advantages of such setup.
> 
> So IMHO a better way to do it is to export each lv as
> a separate disk and make one single partition of whole
> such disk in domU:
> /dev/vg/lv1 -> /dev/hda -> /dev/hda1 --> /
> /dev/vg/lv2 -> /dev/hdb -> /dev/hdb1 --> /var
> /dev/vg/lv3 -> /dev/hdc -> /dev/hdc1 --> /home
> 
> Resizing is extremly easy (lvextend, resize2fs)
> and it can be done online if ext3 is used.
> 
> The only disadvantage is you can't mount such filesystem
> directly, you need to run 'kpartx -a' first to map nested
> domuU block devies in dom0. But that's also pretty easy.

What would be the practical reason for that as opposed to
allocating a bigger LV to contain all partitions?

It seems they are all running across the same spindles, so
there is no real performance improvement. Your splitting
the lanes, but they still merge back before they hit
the disk...

Typically I use one LV for the guest, I put /home on a
NFS share and for high performance apps setup an iSCSI
volume. That for me makes the best use of space while
providing the best performance.

-Ross

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