[linux-lvm] changing protection of lvm2 snapshot origin
karl.kiniger at med.ge.com
Thu Mar 12 15:12:38 UTC 2009
I want to do the following:
* lvcreate -m test_lv -L 4G some_vg
* fill test_lv with a qemu disk image
* lvchange -p r some_vg/test_lv --- I want to make sure that nobody
will ever modify the (future) origin
* lvcreate -s -m test_lv_snap -L 1G some_vg/test_lv
* Use the some_vg/test_lv_snap playing around with qemu, virtualbox, vmware.
Later I want to apply the snapshot contents to the origin -
preferably using the highly efficient dm-merge program (from this
mailing list) taking contents from the snapshot exception table.
Unfortunately lvchange does not me to change the permissions if there
is an active snapshot.
* lvchange -p rw some_vg/test_lv --- I have to remove the snapshot
first. For now I have to copy the exception table contents
elsewhere, remove test_lv_snap and then I am able to apply
the changes. It may be possible with an additional dmsetup
mapping, I would like to avoid that.
So how to avoid the copy of the exception table contents ?
PS: being able to save and re-apply an cow exception table is really
convenient when playing around with bad software. I have hacked
dm-merge to save a whole exception table to a disk file which can
be also compressed for archiving purposes. A few hours work on
e.g Windows XP (80 GB "disk") results in about 50..70 MB compressed
exception table contents (of course depending on what you are doing).
I am also planning to extend dm-merge to be able to save the
contents of a dm snapshot origin which is related to the snapshot
exception table to a file in order to enable me to roll back the
origin to a previous version. I have tried xdelta3 but found it to
be highly inefficient in some cases.
D.I. Karl Kiniger mailto:karl.kiniger at med.ge.com
Tel: (++43) 7682-3800-710 Voip(GE): 1662 710
Fax: (++43) 7682-3800-47 C: +43 6991 3800 710
GE Medical Systems Kretztechnik GmbH & Co OHG - Tiefenbach 15 – A-4871 Zipf
Landesgericht Wels FN 222387s – UID (VAT-ID): ATU54086108 - DVR: 2111103 – ARA: 12816
Persönlich haftende Gesellschafterin: GE Medical Systems Kretztechnik GmbH
Tiefenbach 15 – A-4871 Zipf - Landesgericht Wels FN 218689b
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