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Re: [linux-lvm] Snapshots of snapshots are not supported yet



Dne 10.7.2013 22:12, markw mohawksoft com napsal(a):
Dne 10.7.2013 16:45, markw mohawksoft com napsal(a):

As I said -  btrfs has some kind of functionality you are looking for,
Or you may start to help with lvm project...
(Or thin-provisioning tools in this case)

Zdenek

That link you sent was good, I am looking in to it, it may provide a large
amount of help.

One last thing.... :-)

Now imagine this:

create disk0

Activity on disk0

Take a snapshot
disk0 -> disk0_snap0

Activity on disk0

take a snapshot
disk0 -> disk0_snap1

(We will now use the differential between snap1 and snap0 to represent
what needs to be backed up from snap1)

This leaves us with something that looks like this:

disk0 --> disk0_snap0
        -> disk0_snap1

Will we need to remap the parentage of disk0_snap0 so it looks something
like this?

disk0 -> disk0_snap1 -> disk0_snap0
(Is this possible with dmsetup?)

Or could we have many (order of hundreds or thousands) of snaps directly
on disk0 and not impact performance?


Thin provisioning is written to support this. Note - you do not need to have snapshots present as active devices - i.e. you could snapshot your device every hour.

If you want to discover diff between _snap0 and _snap1 - you have number of choices - if you want to know 'filesystem' diff or block device diff.
Block device  diff could be detected by doing a diff in metadata between
btree for _snap0 and _snap1.

Also there are projects like 'snapper' for filesystem diffs.

Zdenek


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