[linux-lvm] mirror and snapshot incompatible

[Jonathan Brassow]

No, there isn't a reason LVM prevents it, other than we haven't gotten  
to it yet.  That being said... because we haven't gotten to it yet  
also means there probably hasn't been a whole lot of testing of such a  
configuration.  Therefore, it's difficult to quantify the safety.

  brassow

On Oct 28, 2008, at 7:32 PM, Yoav wrote:

> I know how to do it through device-mapper.  I'm just worried that  
> maybe there's a reason why lvm prevents it.  Are you aware of such  
> reason, or is it safe?
>
> Jonathan Brassow wrote:
>> 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.)
>>
>> brassow
>>
>> 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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>>> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>>
>> _______________________________________________
>> linux-lvm mailing list
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>> https://www.redhat.com/mailman/listinfo/linux-lvm
>> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>
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