"create snapshots of any block device"

[Hauke Laging <mailinglisten@hauke-laging.de>]

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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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