Dne 10.7.2013 05:45, markw@mohawksoft.com napsal(a):
One more annoying question, if you have the patience.
Suppose I create a thin provisioned volume, say disk0.
I take a snapshot of disk0 and name it disk0_snap0
After a number of changes I then take another snapshot, and call it
disk0_snap1
Is the thin provisioning stuff smart enough to realize that disk0_snap0
should be rewired to reference disk0_snap1 as its origin? It would look
like this:
disk0 -> disk0_snap1 -> disk0_snap0
What I would like to see is something like this:
disk0 -> disk0_snap2 -> disk0_snap1 -> disk0_snap0
Create disk0_snap3
disk0 -> disk0_snap3 -> disk0_snap2 -> disk0_snap1 -> disk0_snap0
Where all writes to disk0 result in CoW to disk0_snap3 and the remaining
snaps remain unchanged.
Here is the kicker, I want to perform a differential backup on disk0_snap3
and disk0_snap2. Suppose I already recreated disk0_snap2 on some server.
I now want to update it to disk0_snap3. I need to get a block list from
disk0_snap2 and disk0_snap3, then generate a list of blocks needed to
permute snap2 to snap3.
Any info?
Yes - differential snapshot will be supported through thin provisioning
target - where you will be able to make a simple diff just by reading
metadata - it will be essential piece of replication.
AFAIK Joe has this in plan for some time - and there was even some
announcement from some third-party developer to support this.
There is not going to be any upstream support for doing this with
old-snaps in foreseeable future.
Also keep in mind your idea of using old-snap of snap of snap would be very
slow and fragile to use.
Zdenek
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