[linux-lvm] more vg problems or oddities...not using dmsetup remove seems to be bad?

Linda A. Walsh lvm at tlinx.org
Mon Sep 12 04:08:03 UTC 2011

Here's a sadistic (or masochistic, maybe both, if I do it to myself)... 

If I start a snapshot today... (or if one is already running)...

And the merge happens, will the snapshot take today have the
data to undo the merge?

Stuart D. Gathman wrote:
> On Sun, 11 Sep 2011, Stuart D. Gathman wrote:
>> On Sun, 11 Sep 2011, Linda A. Walsh wrote:
>>> tried -- merging it...
>> Ooops.  You likely did not want that.  That reverts the origin volume
>> to the snapshot by copying the original data for updated sectors from
>> the snapshot.  This is an extremely useful feature, but *not* when
>> you invoke it accidentally!
>>> I'm wondering if I really want this 'merge' it wants to do...and if 
>>> not, how do I abort it?
>> If it is really delayed until boot (or close), then you have a chance 
>> to abort
>> it, but I don't know how.  I hope an expert answers.  Meanwhile, I'll
>> peruse the man page to see if it talks about delayed merge.
> The man page says:
>   If both the origin and snapshot volume are not open the merge will 
> start
>   immediately.   Otherwise, the  merge  will start the first time 
> either the
>   origin or snap??? shot are activated and both are closed.  Merging a 
> snapshot
>   into an  origin that cannot be closed, for example a root 
> filesystem, is
>   deferred until the next time the origin volume is  activated.  When  
> merging
>   starts, the resulting logical volume will have the origin's name, minor
>   number and UUID.  While  the  merge  is  in progress,  reads  or  
> writes  to
>   the origin appear as they were directed to the snapshot being 
> merged.  When
>   the merge finishes, the merged snapshot is removed.  Multiple 
> snapshots may
>   be specified on the commandline or a @tag may be used to specify 
> multi??? ple
>   snapshots be merged to their respective origin.
> If you have space, I would copy your origin LV while you can.  There is
> nothing about cancelling the merge.  I suspect you could restore the 
> metadata
> backup from before your merge.  But make backups first!
> -- 
>           Stuart D. Gathman <stuart at bmsi.com>
>     Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 
> 591-6154
> "Confutatis maledictis, flammis acribus addictis" - background song for
> a Microsoft sponsored "Where do you want to go from here?" commercial.
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