[CentOS] Best way to take snapshots of iSCSI devices using Open-iSCSI + CentOS

John R Pierce pierce at hogranch.com
Sat Dec 6 11:50:04 UTC 2008


Santi Saez wrote:
> Hi,
>
> I want to take snapshots of a iSCSI devices from a target that hasn't 
> snapshot/cloning capabilities (it's a Infortrend A16E storage array).
>
> What method are you using to make snapshots/clones of iSCSI targets 
> using Open-iSCSI + CentOS? What about using Open-iSCSI + LVM snapshots 
> system? For example:
>
> - Take a LVM snapshot in the initiator with "lvcreate".
> - Give read-only access to the backup server, for the same LUN/volume.
> - In the backup server, mount in read-only mode this snapshot.
> - Take a backup of this snapshot, using dd/tar/rsync for example.
> - Unmount the snapshot in the backup server.
> - Remove this snapshot from the host with "lvremove".
>
> Is there any soft to make this? thanks! NOTE: It's a must, that device 
> snapshots must be in other device.. not in the same target.
>   

as I understand it, LVM snapshots are copy-on-write.   that means the 
data blocks of the LVM snapshot are quite dynamic when the underlying 
original volume is changing.  I do NOT think it would be even remotely 
safe to mount this read only on another environment as that OS wouldn't 
have a clue the underlying LVM stuff was being changed while its reading it.






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