Dne 14.1.2015 v 11:18 Bram Klein Gunnewiek napsal(a):
Thanks for your reply. I tested it out and it does not seem to work (lvm2
version used is 2.02.98-6ubuntu2):
yep - too old for this feature being supported.
lvcreate -n testvolume3 -L 1G vg
lvcreate -n testvolume3_snapshot -s /dev/vg/testvolume3 -l100%ORIGIN
dd if=/dev/zero of=/dev/vg/testvolume3 bs=1G count=1
After this the snapshot is invalid:
testvolume3_snapshot vg swi-I-s-- 1.00g testvolume3 100.00
I checked out the lvm2 source code and found the methods cow_max_extents and
_cow_max_size in snapshot_manip.c. Do these methods calculate the exact max
size of the snapshot meta data?
yes.
It's probably worth to note there has been some related kernel fixes for old
snaps - otherwise there has been theoretical path to create much bigger
snapshots then the origin size was - though it's nearly impossible to reach
such state.
Zdenek
On 01/14/2015 09:34 AM, Zdenek Kabelac wrote:
Dne 14.1.2015 v 08:24 Bram Klein Gunnewiek napsal(a):
Hello,
I am trying to create snapshots of thick volumes that can't break because they
overflow (thin volumes are not an option right now). I can't find information
on how to calculate (in advance) the metadata overhead of a snapshot when all
blocks in the origin volume are changed (e.g. the snapshot is 100% full). Is
there a way to do this?
Recent versions of lvm2 (let's say >= 111) are able to determine this size
automatically - just use: 'lvcreate -s -l100%ORIGIN vg/origin'
Regards
Zdenek
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