[dm-devel] "create snapshots of any block device"
Hauke Laging
mailinglisten at hauke-laging.de
Tue Jan 22 11:12:58 UTC 2013
Hello,
I am a bit surprised to read this:
"Device-mapper allows you, without massive data copying:
*) To create snapshots of any block device [...]"
here:
http://www.kernel.org/doc/Documentation/device-mapper/snapshot.txt
Isn't that at least misleading? Is it really possible to create a snapshot of
e.g. /dev/sda5 without creating an *additional* device as snapshot origin?
I export LVs to a VM where they appear as regular disks so that I cannot use
LVMs snapshot integration. Thus I create a dm device with a linear mapping to
each of these disks and mount the dm device, not the disk.
I just had the idea to create these dm layer devices as snapshot-origins from
the start (instead of loading this target when a snapshot is really going to
be created). Is there anything to be said against this? Is there any reason at
all to use linear instead of snapshot-origin for devices with just one target
(except for possible confusion)?
Hauke
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