[linux-lvm] Block-Level Backup
Bill Rugolsky Jr.
brugolsky at telemetry-investments.com
Thu Aug 7 11:33:01 UTC 2003
On Thu, Aug 07, 2003 at 04:54:21PM +0100, Joe Thornber wrote:
> This scheme only works if you don't use the device while you are
> taking an incremental backup. I think the real solution will be based
> around snapshots.
Right. But I think the point is this: one won't mind keeping multiple
(tower of hanoi) long-lived (week or more) block change indices, because
the performance impact should be very low.
When it it time to do an actual backup, we simultaneously create a
new block change index, take a regular snapshot, and freeze (or copy)
the block-change index of interest. Then we just back up the blocks
from the snapshot volume indicated in the frozen block-change index and
then delete the frozen block-change index and the snapshot volume.
For a typical filesystem, the snapshot volume persists for seconds to
minutes while the data is copied, not the tens of minutes to hours often
required to traverse the whole device with a tool like dump(8).
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