[linux-lvm] mirror and snapshot incompatible

Jonathan Brassow jbrassow at redhat.com
Tue Oct 28 20:56:46 UTC 2008

It is possible to do all the things you are asking through device- 
mapper... but there is no easy way to do it.  (and LVM does not yet  
have the capabilities to manage this yet either.)


On Oct 27, 2008, at 9:28 PM, Yoav wrote:

> According to lvcreate, a snapshot of a mirrored volume cannot be  
> created ("Snapshots and mirrors may not yet be mixed").  However,  
> devmapper does not seem to have the same limitation when used  
> directly (not through lvm).
> Is there a current reason for lvcreate to enforce this rather harsh  
> limitation?
> What are the risks I'm taking by manually creating a dm-snapshot  
> from a dm-mirror device?  (of course I'm also replacing the dm- 
> mirror device with a snapshot-origin of the actual dm-mirror device).
> If there is an actual reason for preventing this, what is the  
> suggested way to consistently backup a mirror volume?  Is there a  
> way to temporarily take one of the mirror "legs" (mimage devices)   
> offline in order to back it up, and resync it later?
>   Yoav
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