On Thu, Sep 28, 2017 at 2:00 PM, Joshua Judson Rosen <roz...@hackerposse.com > wrote:
> On 09/28/2017 01:46 PM, Tom Buskey wrote: > > I work with OpenStack. It manages images in Glance which sit above its > object storage, Swift. > > > > On the POC clouds, you can use LVM as a backend for Glance. > Snapshotting is *very* slow. 30 minutes for a snap of a > > 80GB VM that's shutdown. > > OK..., that surprises me. A lot. > > > For comparison, I just made an LVM snapshot of a volume 50% larger than > that, that's *in use* > (and mostly not in cache, if that even makes a difference, since my > buffer+cache shows as only 17GB *total*), > and the whole operation took only a fraction of a second: > > rozzin@zuul:~ $ time sudo lvcreate --name home_snap --size 128G > --snapshot zuul-vg/home > Using default stripesize 64.00 KiB. > Logical volume "home_snap" created. > > real 0m0.349s > user 0m0.028s > sys 0m0.060s > > > How in the world does that translate to 30-minutes (*5 thousand* x time) > for a volume only 0.63x as big? > > When you say "snapshotting on top of LVM", does that entail actually > making a full copy > after the LVM snapshot is made--or something like that? > > I'm not exactly sure what OpenStack VM snapshots are doing under the covers. I'm sure it's not an LVM snapshot. Openstack VMs use .qcow2 files, which are COW. There is a copy/convert process in the Openstack process so the image the VM uses can be resumed and you can redeploy the snapshot as a new VM or even copy/launch it on another system. I misspoke about LVM for Glance/Swift. The backend for the images are on top of a filesystem in the POC clouds. LVM is used for Cinder, the block image store. Ceph is often used to drop in replace LVM for Cinder and files for Swift objects.
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