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Date: Wed, 10 Sep 2014 16:47:14 -0700
From: Ross Boylan <ross@biostat.ucsf.edu>
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Subject: Re: [dm-crypt] expanding encrypted volume/growing the volume
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To: Robert Nichols <rnicholsNOSPAM@comcast.net>
Cc: dm-crypt@saout.de

Thanks for looking things over.
Snapshot info below.
On Wed, Sep 10, 2014 at 05:52:13PM -0500, Robert Nichols wrote:
> On 09/10/2014 05:44 PM, Robert Nichols wrote:
>> Yes, I would merge the snapshot back into the base volume and close the
>> snapshot before extending the filesystem.  Otherwise, the enlarged
>> filesystem structure will exist only in the snapshot.  I suppose an
>> alternative would be to merge the current snapshot, start a new snapshot,
>> and the enlarge the filesystem.  If anything went wrong during the resizing,
>> you could just discard the snapshot and be right back where you were with
>> the filesystem. Merge that snapshot once you've determined that all went
>> well.
>
> ALERT:  I'm thinking of that snapshot backwards, because that's how I most
> often use them (create the snapshot, mount the snapshot instead of the base
> volume, perform the experiment, then throw the snapshot away and mount the
> base volume again to forget the experiment.)
>
> Since I don't know the age or purpose of that snapshot, I don't know whether
> you would want to close it.  It would be a snapshot of the pre-expansion
> filesystem.


These are read-only snapshots created for the backup program.  The
backup program backs up the file system as seen through the snapshot..

It does seem as if it would be easy for something to go wrong if the
snapshot were active while the underlying volume grew.  At a minimum,
growing the file system would presumably use up a lot of space in the
snapshot.

Ross