[linux-lvm] exposing snapshot block device

Dalebjörk, Tomas tomas.dalebjork at gmail.com
Tue Oct 22 10:47:30 UTC 2019


Hi

When you create a snapshot of a logical volume.

A new virtual dm- device will be created with the content of the changes 
from the origin.

This cow device can than be used to read changed contents etc.


In case of an incident, this cow device can be used to read back the 
changed content to its origin using the "lvmerge" command.


The question I have is if there is a way to couple an external cow 
device to an empty equaly sized logical volume,

so that the empty logical volume is aware of that all changed content 
are placed on this attached cow device?

If that is possible, than it will help making instant recovery of LV 
volumes from an external source using native lvmerge command, from for 
example a backup server.


[EMPTY LOGICAL VOLUME]
         ^
         |
      lvmerge
         |

[ATTACHED COW DEVICE]

Regards Tomas

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