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Re: [libvirt] [PATCH]: vgscan before doing logical pool discovery



On Tue, Nov 04, 2008 at 06:32:37PM +0100, Chris Lalancette wrote:
> Assume that you have an iSCSI target available, and on that iSCSI target 1 LUN
> is exported.  On that 1 LUN, you have an LVM volume group (say, myvg), with 2
> logical volumes (say, lv1 and lv2).  Now you execute the following sequence of
> commands:
> 
> 1)  virsh define iscsi_pool.xml
> 2)  virsh start iscsi_pool
> 3)  virsh find-storage-pool-sources-as logical
> 
> With that sequence, you would expect step 3) to return XML similar to:
> 
> <sources><source><name>myvg</name><device path='/dev/sdb'/></source></sources>
> 
> However, what you instead get is: <sources/>.  That's because if you just try to
> do storage pool discovery on a logical pool without ever touching the logical
> pool in any fashion, pvs (what we use to do discovery) doesn't return anything.
>  If you touch the logical volume group at all (say, with vgscan), they then
> suddenly appear.  To make sure we see all of the potential volume groups when
> doing pool discovery, make sure to run vgscan before we run pvs.  With this
> patch in place, logical discovery just does the right thing.

ACK, this makes total sense.

Daniel
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