[dm-crypt] expanding encrypted volume/growing the volume
arno at wagner.name
Wed Sep 10 07:16:10 CEST 2014
On Wed, Sep 10, 2014 at 06:30:24 CEST, Ross Boylan wrote:
> A little more on resizing on the bottom, with related excerpts above it.
> At least one piece of advice on the internet does luksClose, luksOpen
> AND cryptsetup resize:
That one is broken. Or rather the "resize" does nothing to
the LUKS container. It may just be there for the --verbose.
Really, there is no "partition size" field anywhere in the
LUKS header and it is not needed.
A brief look into the man-page shows what "resize" does:
Resizes an active mapping <name>.
If --size (in sectors) is not specified, the size of the under‐
lying block device is used. Note that this does not change the
raw device geometry, it just changes how many sectors of the raw
device are represented in the mapped device.
As to my other comments, I see now that you left out one very
critical piece of information: You want to do this _online_.
(Or I read over it. If so, sorry.) That is generally not a
good idea, but that is indeed one of the scenarios where you
would need "cryptsetup resize". (But not after a luksOpen.
luksOpen reads the device-size from the kernel anyways.)
You would need to extend the partition first, make the kernel
aware of the new size (I gather lvextend does that, personally I
stay away from LVM, far too complicated...), call
"cryptsetup resize <device>" and then extend the filesystem
in the LUKS container. If all of that works, good. If anything
goes wrong, I hope you refreshed that backup and have the time
to restore from it.
Generally, in a situation where you have low downtime needs,
you should have a second identical machine with automatic
fail-over anyways. There you can take down one machine,
make the changes offline, test them, bring it back up
and then fail-over to it. Repeat with the second one.
If you do not have low downdime needs, do this offline,
as the risk of doing some real damage is lower.
Arno Wagner, Dr. sc. techn., Dipl. Inform., Email: arno at wagner.name
GnuPG: ID: CB5D9718 FP: 12D6 C03B 1B30 33BB 13CF B774 E35C 5FA1 CB5D 9718
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