archive mirror
 help / color / mirror / Atom feed
From: Zdenek Kabelac <>
To: "Tomas Dalebjörk" <>
Cc: LVM general discussion and development <>
Subject: Re: [linux-lvm] how to convert a disk containing a snapshot to a snapshot lv?
Date: Tue, 21 Dec 2021 16:30:48 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Dne 21. 12. 21 v 15:44 Tomas Dalebjörk napsal(a):
> hi
> I think I didn’t explain this clear enough
> Allthe lvm data is present in the snapshot that I provision from our backup system
> I can guarantee that!
> If I just mount that snapshot from our backup system, it works perfectly well
> so we don’t need the origin volumes in other way than copying back to it
> we just need to reanimate it as a cow volume
> mentioning that all data has been changed
> the cow is just referencing to the origin location, so no problem there
> All our data is in the cow volume, not just the changes
> just to compare
> if you change just 1 byte on every chunksize in the origin volume, than the snapshot will contain all data, plus some meta data etc.
> That is what I talk about here.
> So how do I retach this volume to a new server?
> as the only argument acceptable argument by the lvconvert is vg/s1 ?
> That assumes that vg/s1 is present
> so how to make it present?


As said in my previous post - the 'format' of data stored on COW storage 
(which is the 'real' meaning of snapshot LV) does NOT in any way resembles the 
'normal' LV.

So the COW LV could be really ONLY use together with 'snapshot' target.

The easiest way how to 'copy' this snapshot to normal LV is like this:

lvcreate -L size  -n newLV  vg

dd if=/dev/vg/snapshotLV  of=/dev/vg/newLV  bs=512K

(so with 'DD' you copy data in 'correct' format)

You cannot convert snapshot LV to 'normal' LV in any other way then to merge 
this snapshot LV into your origin LV  (so origin is gone)
(lvconvert --merge....)

You can also  'split' snapshot COW LV and 'reattach' such snapshot to other LV 
- but this requires rather good knowledge about whole functioning of this 
snapshotting - so you know what can you do and what can you expect. But I'd 
likely recommend  'dd'.
You cannot use 'splitted' COW LV for i.e. filesystem - as it contains 'mixed' 
snapshot metadata and snapshot blocks.

Old snapshot meaning was - to take 'time consistent' snapshot of LV which then 
you can use for i.e. taking backup....



linux-lvm mailing list
read the LVM HOW-TO at

  reply	other threads:[~2021-12-21 15:31 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-19 16:43 [linux-lvm] how to convert a disk containing a snapshot to a snapshot lv? Tomas Dalebjörk
2021-12-20 14:51 ` Phillip Susi
2021-12-21 13:46 ` Zdenek Kabelac
2021-12-21 14:44   ` Tomas Dalebjörk
2021-12-21 15:30     ` Zdenek Kabelac [this message]
2021-12-21 16:12       ` Tomas Dalebjörk
2021-12-22 10:40         ` Zdenek Kabelac
2021-12-28  5:04         ` Stuart D Gathman
2021-12-28  6:40           ` Tomas Dalebjörk
2021-12-29 13:35             ` Stuart D Gathman
2021-12-21 19:23     ` Phillip Susi

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).