This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --RH6VeLgsV4aCdphWinrtX2PUWEbHMwDj6 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 09/19/2014 12:10 PM, R P Herrold wrote: Close. The terminology intended is indeed high water mark, but more as a measure of when the underlying storage must be enlarged to avoid pausing due to ENOSPC. There won't be actual content loss, as long as the guest is configured to pause on write errors, and the guest can be resumed after storage is enlarged whether or not the high water mark was used to attempt to pre-emptively grow the storage before actually running out of space. On the libvirt list, we decided to go with calling it 'allocation' reporting, rather than 'watermark', because of the confusion in the term watermark. Dynamic storage is common with VDSM which tracks guest storage by using host LVM partitions formatted with qcow2. Qcow2 files can be sparse by nature, so, for example, you can allocate a backing chain base <- active, where base is 30G, and active starts out as a 10G partition. As the guest causes more and more COW to differ from base, qemu will report higher and higher allocation values, and if management is carefully tracking these values, it can resize the LVM volume to 15G prior to pausing the guest when qemu can't write more qcow2 metadata. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --RH6VeLgsV4aCdphWinrtX2PUWEbHMwDj6 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" --RH6VeLgsV4aCdphWinrtX2PUWEbHMwDj6--