[Ovirt-devel] Modeling LVM storage

[Chris Lalancette]

Steve Ofsthun wrote:
> Chris Lalancette wrote:
>> sseago and I (and variously, other folks) had a somewhat longish
>> conversation on IRC today about carving up storage with LVM.  This is the
>> second time we've beaten this horse, so hopefully we are somewhat OK now.
>> The basic idea is that, given an iSCSI LUN (and SCSI and FC LUNs in the
>> future), we want to either:
>> 
>> 1)  Assign the entire LUN to a guest (this is the way that ovirt works
>> right now) 2)  Carve up the LUN using LVM, and then hand out individual
>> logical volumes to guests.
> 
> How do you plan to distinguish between LVM PVs/LVs created by ovirt/libvirt
> on iscsi LUNs from LVM PVs/LVs created by guest OSes on directly connected
> iscsi LUNs?  Just blindly running pvscan will run into all sorts of trouble.

This actually shouldn't be a problem, I don't think.  When we assign a whole LUN
to a guest, the guest will in all likelihood lay down a partition table.  Since
the partition table isn't a valid LVM partition, scanning that LUN won't have
any LVM metadata on it.  Now, if you have the case where a guest *doesn't* lie
down a partition table, and directly uses the whole disk as LVM, I guess we
could run into a problem.  I don't know how common a case that is, but at least
in Fedora/RHEL land, we never do that by default.

-- 
Chris Lalancette