<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Sep 28, 2017 at 2:00 PM, Joshua Judson Rosen <span dir="ltr"><<a href="mailto:rozzin@hackerposse.com" target="_blank">rozzin@hackerposse.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class="">On 09/28/2017 01:46 PM, Tom Buskey wrote:<br>
> I work with OpenStack. It manages images in Glance which sit above its object storage, Swift.<br>
><br>
> On the POC clouds, you can use LVM as a backend for Glance. Snapshotting is *very* slow. 30 minutes for a snap of a<br>
> 80GB VM that's shutdown.<br>
<br>
</span>OK..., that surprises me. A lot.<br></blockquote><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
For comparison, I just made an LVM snapshot of a volume 50% larger than that, that's *in use*<br>
(and mostly not in cache, if that even makes a difference, since my buffer+cache shows as only 17GB *total*),<br>
and the whole operation took only a fraction of a second:<br>
<br>
rozzin@zuul:~ $ time sudo lvcreate --name home_snap --size 128G --snapshot zuul-vg/home<br>
Using default stripesize 64.00 KiB.<br>
Logical volume "home_snap" created.<br>
<br>
real 0m0.349s<br>
user 0m0.028s<br>
sys 0m0.060s<br>
<br>
<br>
How in the world does that translate to 30-minutes (*5 thousand* x time)<br>
for a volume only 0.63x as big?<br>
<br>
When you say "snapshotting on top of LVM", does that entail actually making a full copy<br>
after the LVM snapshot is made--or something like that?<br>
<span class=""><br></span></blockquote><div><br></div><div>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.</div><div><br></div><div>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.</div></div></div></div>