Vijai Babu Madhavan, Thu, 11 Jan 2007 11:18:13 -0700, wrote:
The problem of DM snapshots with multiple snapshots have been discussed
in the lists quiet a bit (Most recently @
https://www.redhat.com/archives/dm-devel/2006-October/msg00034.html).
We are currently in the process of building a DM snapshot target that scales
well with many snapshots (so that the changed blocks don't get copied to each
snapshot). In this process, I would also like to validate an assumption.
Today, when a single snapshot gets created, a new cow device of a given size
is also created. IMO, there are two problems with this approach:
a) It is difficult to predict the size of the cow device, which requires a prediction
of the number of writes would go into the origin volume during the snapshot
life cycle. It is difficult to get this prediction right, as very high value reduces
utilization and low value increases the chances of snapshot becoming full.
b) A new cow device needs to be created every time.
Hi,
Any news on that?
Still, with multiple snapshots write performance degrades linearly - is
any work done to change that anytime soon?
--
Tomasz Chmielewski
http://wpkg.org
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