[linux-lvm] exposing snapshot block device

[Tomas Dalebjörk]

it worked

I missed the -Zn flag


Sent from my iPhone

> On 7 Sep 2020, at 21:56, Tomas Dalebjörk <tomas.dalebjork at gmail.com> wrote:
> 
> hi 
> I tried all these steps
> but when I associated the snapshot cow device back to an empty origin, and typed the lvs command
> the data% output shows 0% instead of 37% ?
> so it looks like that the lvconvert -s vg1/lvsnap vg1/lv0 looses the cow data?
> 
> perhaps ypu can guide me how this can be done?
> 
> btw, just to emulate s full copy, I executed the 
> dd if=/dev/vg0/lv0 of=/dev/vg1/lv0 
> before the lvconvert -s, to make sure the last data is there
> 
> and than I tried to mount the vg1/lv0 which worked fine
> but the data was not at snapshot view
> even mounting vg1/lvsnap works fine
> but with wrong data
> 
> confused over how and why vgmerge should be used as vgsplit does the work?
> 
> regards Tomas
> 
> Sent from my iPhone
> 
>> On 7 Sep 2020, at 18:42, Zdenek Kabelac <zkabelac at redhat.com> wrote:
>> 
>> Dne 07. 09. 20 v 18:34 Tomas Dalebjörk napsal(a):
>>> thanks for feedback
>>> so if I understand this correctly
>>> # fallocate -l 100M /tmp/pv1
>>> # fallocate -l 100M /tmp/pv2
>>> # fallocate -l 100M /tmp/pv3
>>> # losetup —find —show /tmp/pv1
>>> # losetup —find —show /tmp/pv2
>>> # losetup —find —show /tmp/pv3
>>> # vgcreate vg0 /dev/loop0
>>> # lvcreate -n lv0 -l 1 vg0
>>> # vgextend vg0 /dev/loop1
>>> # lvcreate -s -l 1 -n lvsnap /dev/loop1
>>> # vgchange -a n vg0
>>> # lvconvert —splitsnapshot vg0/lvsnap
>>> # vgreduce vg0 /dev/loop1
>> 
>> 
>> Hi
>> 
>> Here you would need to use 'vgsplit' rather - otherwise you
>> loose the mapping for whatever was living on /dev/loop1
>> 
>>> # vgcreate vg1 /dev/loop2
>>> # lvcreate -n lv0 -l 1 vg1
>>> # vgextend vg1 /dev/loop1
>> 
>> And  'vgmerge'
>> 
>> 
>>> # lvconvert -s vg1/lvsnap vg1/lv0
>>> not sure if the steps are correct?
>> 
>> 
>> I hope you realize the content of vg1/lv0 must be exactly same
>> as vg0/lv0.
>> 
>> As snapshot COW volume contains only 'diff chunks' - so if you
>> would attach snapshot to 'different' lv - you would get only mess.
>> 
>> 
>> Zdenek
>>