[linux-lvm] creating DD copies of disks
list at xenhideout.nl
Sat Sep 17 07:29:16 UTC 2016
I want to ask again:
What is the proper procedure when duplicating a disk with DD?
- after duplication you cannot update a PV with pvchange -u because it
will supersede your duplicate with the original and not do anything
So to do that you need to boot off a different system, deactivate loaded
vgs (if any) and then pvchange -u the duplicate PV.
- my experience indicates that pvchange -ay on a PV that contains a
duplicate VG, even if it has a different UUID, but with an identical
name, creates problems.
I mean that anytime you load a VG with the same name you get issues. VG
names are often standardized between installs, so that Ubuntu might have
"ubuntu-vg" as the name and kubuntu might have "kubuntu-vg" as the name.
So if you then load two of those disks in the same system, you instantly
If the system were to auto- or temporary-rename an offending 2nd VG it
wouldn't be so bad. But usually you have to vgrename rename your current
VG in advance of loading a second disk.
Which isn't exactly as intended, because now you are changing your local
name to make room for a second system, when it should really be the
other way around.
In the end I feel I have to do:
To get something that will at least not bug me when both systems are
loaded at the same time.
This then renders it impossible to use it as a backup because any other
disk referencing the PV will not find it because the UUID has changed.
Now you would first have to reverse these operations (particularly the
vgrename and pvchange -u) towards the data of the first disk (the
original) to be able to use the device again.
All of that is not very resilient. Now both PV UUIDs and VG names have
to be unique.
Particularly I wonder how easy it is to point an existing VG to a disk
that has a new (duplicate) PV and tell it: use that one from now on.
I mean: how can I add a disk that has a duplicate PV with a different
UUID and add it to the VG in such a way that it replaces the references
that VG has for the old PV?
But also: what ought you to do if creating a mirror copy? (duplicate
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