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Re: [linux-lvm] Question before merging snapshot



On 09/02/2013 10:21 PM, Ron Schneider wrote:

Hi all,

Situation:

I have a volume A that contains production data.
For an experiment I created volume a' from A using
the snapshot function.
I then used a' for my experiment, which went very well.

Now I want to merge snapshot a' back into A. I have read that the merge
will effectively make A to be what a' was before, then a' will
disappear. However, all examples that I found on the net referred to
making snapshot a' then making changes to the origin A and finally using
--merge to revert A back to a'.
In my case though, I used the snapshot a' for writing instead of origin
A. I just want you to confirm that --merge will function the same way
nevertheless, thus making the modified content of a' appear in the
origin LV A.
Of course I will backup everything before the merge but I'd like to save
myself unnecessary recovery cycles so I thought I'd just ask the pros
beforehand - just to be sure.

Hi, what's in the snapshot will become content of the origin, regardless where the writes go.

When writing to origin, merge will revert the changes made to origin since snapshot was taken.

When writing to snapshot, merge will promote the changes made in the snapshot to the origin.

When writing to both, changes to origin will be reverted and changes made in snapshot will be promoted.

-- Marian




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