[openstack-dev] Announcing Ekko -- Scalable block-based backup for OpenStack
samuel at yaple.net
Wed Feb 3 15:27:43 UTC 2016
On Wed, Feb 3, 2016 at 2:37 PM, Duncan Thomas <duncan.thomas at gmail.com>
> On 3 February 2016 at 16:32, Sam Yaple <samuel at yaple.net> wrote:
>> Looking into it, however, shows Cinder has no mechanism to delete backups
>> in the middle of a chain since you use dependent backups (please correct me
>> if I am wrong here). This means after a number of incremental backups you
>> _must_ take another full to ensure the chain doesn't get to long. That is a
>> problem Ekko is purposing to solve as well. Full backups are costly in
>> terms of IO, storage, bandwidth and time. A full backup being required in a
>> backup plan is a big problem for backups when we talk about volumes that
>> are terabytes large.
> You're right that this is an issue currently. Cinder actually has enough
> info in theory to be able to trivially squash backups to be able to break
> the chain, it's only a bit of metadata ref counting and juggling, however
> nobody has yet written the code.
And here we get to the meat of the matter. Squashing backups is awful in
object storage. It requires you to pull both backups, merge them, then
reupload. This also has the downside of casting doubt on a backup since you
are now modifying data after it has been backed up (though that doubt is
lessened with proper checksuming/hashing which cinder does it looks like).
This is the issue Ekko can solve (and has solved over the past 2 years).
Ekko can do this "squashing" in a non-traditional way, without ever
modifying content or merging anything. With deletions only. This means we
do not have to pull two backups, merge, and reupload to delete a backup
from the chain.
> Luckily, digging into it it appears cinder already has all the
>> infrastructure in place to handle what we had talked about in a separate
>> email thread Duncan. It is very possible Ekko can leverage the existing
>> features to do it's backup with no change from Cinder. This isn't the
>> initial priority for Ekko though, but it is good information to have. Thank
>> you for your comments!
> Always interested in better ways to solve backup.
Thats the plan!
> Duncan Thomas
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