[linux-lvm] how to copy a snapshot, or restore snapshot without deleting it

[Davis, Matthew]

Hi Zdenek,

What do you mean "it's origin is already gone"?
It is a snapshot of centos/root, which still is there. (I have since modified centos/root)
So the origin is still there.

I think it's because I merged the copy of the snapshot. If I merge the original snapshot, the copy remains and it's origin changes.
That seems to work.

* make snapshot fresh1
* change contents of root
* copy fresh1 to fresh2
* merge fresh1
* reboot
* root is now restored to how it was originally
* fresh 2 now has origin root

That works.
(Although I get a daunting error message every time I create a snapshot, and sometimes I get error messages on merge, but it works most of the time.)

Regards,
Matt

________________________________________
From: Zdenek Kabelac <zkabelac at redhat.com>
Sent: Thursday, 17 January 2019 12:55:59 AM
To: Davis, Matthew; LVM general discussion and development
Subject: Re: how to copy a snapshot, or restore snapshot without deleting it 
 
Dne 16. 01. 19 v 0:03 Davis, Matthew napsal(a):
> Hi Zdenek,
> 
> Here's what I see with `sudo lvs -a`. (My snapshots are actually called `fresh` and `fresh2` not `mySnap`)
> 
> ```
>    LV              VG     Attr       LSize   Pool   Origin Data%  Meta%  Move Log Cpy%Sync Convert
>    fresh           centos Vwi---tz-k  <1.46t pool00
>    fresh2          centos Vwi---tz-k  <1.46t pool00 fresh

So these both LVs are snapshots  (since they were created with  s(k)ipped 
activation - however 'fresh' LV cannot be merged anymore  as it's origin is 
already gone.

But  'lvconvert --merge  centos/fresh2'  should work - yet you need to 
manually drop 'k' flag (via lvchange).

So to have 'working' merge - you have to see something in the 'Origin' field.
If the Origin field is already 'empty' you can't be merging such LV even when 
it was originally created as 'snapshot'.

Also note that thin snapshot merging is nothing else then a bit more 'smart' 
rename.

Zdenek