On Mon, Jan 31, 2011 at 10:08:31PM -0800, Sage Weil wrote:
> A few use cases for all of this:
> - "golden" VM images
> - writeable snapshots
> - image migration between pools
> - pause io
> - mark parent read-only
> - create "child" image
> - unpause io, redirect to the new child
> (these steps are all fast and O(1)!)
> - asynchronously copy-up parent blocks to the child (this is O(n))
> - once this is done, remove the child's parent reference and discard
> the parent
Two things to add:
- creating something that can be later used to do lazy deduplication
in the background would be good; you don't always "start from the
golden master", but you still have images that are 99% identical.
- the "child has zero extents that should not be read from master"
case would happen mostly by TRIM operations, these days.
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