Hello,
At OVH we're heavily utilizing snapshots for our backup system. We think
there's an interesting optimization opportunity regarding snapshots I'd like
to discuss here.
The idea is to introduce a concept of a "lightweight" snapshots - such
snapshot would not contain data but only the information about what has
changed on the image since it was created (so basically only the object map
part of snapshots).
Our backup solution (which seems to be a pretty common practice) is as follows:
1. Create snapshot of the image we want to backup
2. If there's a previous backup snapshot, export diff and apply it on the
backup image
3. If there's no older snapshot, just do a full backup of image
This introduces one big issue: it enforces COW snapshot on image, meaning
that original image access latencies and consumed space increases.
"Lightweight" snapshots would remove these inefficiencies - no COW
performance and storage overhead.
At first glance, it seems like it could be implemented as extension to
current RBD snapshot system, leaving out the machinery required for
copy-on-write. In theory it could even co-exist with regular snapshots.
Removal of these "lightweight" snapshots would be instant (or near instant).
So what do others think about this?
--
Piotr Dałek
piotr.dalek@xxxxxxxxxxxx
https://www.ovhcloud.com
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