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[linux-lvm] Re: lvm partition on lv

Randall Smith wrote:
Warning:  This may be insane.

I like the flexibility of LVM and try to use it wherever it's feasible. In this case, I'd like a Xen guest OS to have control over it's LV's. The method I usually see for using LVM with Xen is to create an LV and a filesystem on it. I would like to instead create an LV and partition it with an LVM partition and maybe other partition types. Just to test this I did the following:

1. lvcreate -L 100M -name test vg1
2. cfdisk /dev/vg1/test
3. create LVM partition on entire device
4. pvcreate /dev/vg1/test
5. vgcreate vg2 /dev/vg1/test
6. vgchange -ay /dev/vg2
7. lvcreate -L 50M -n testlv vg2
8. mkfs.ext3 /dev/vg2/testlv
9. mkdir /mnt/test
10. mount /dev/vg2/testlv /mnt/test

And it worked!  Cool!

Let's say on /dev/vg1/test I had one LVM partition and one ext3 partition. How can I access those separate partitions since it's only one device (/dev/vg1/test)? Normally, a partitioned block device (/dev/hda) would show up like /dev/hda1, dev/hda2, etc.

In the example above, I'm partitioning the LV and using the partition on the same system, which is useless. What I will be doing is giving the disk image /dev/vg1/test to a Xen guest so it can have it's own VG and LVs. Are there potential problems I should look out for and/or tweaking I should do to make this work optimally?

/dev/vg1/test is used as a disk for the Xen guest OS. The guest then recognizes vg2 on /dev/vg1/test. By default, the host will also recognize and activate vg2. Is there a problem with this and should I somehow configure the host not to activate vg2? I know this may be confusing, but it's very useful. I actually have it working now with several LVs on vg2. So I've got PV->VG->LV->PV->VG-(LVs).


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