From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (ext-mx29.extmail.prod.ext.phx2.redhat.com [10.5.110.70]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C6CB5165D7 for ; Tue, 22 Oct 2019 10:47:35 +0000 (UTC) Received: from mail-lj1-f172.google.com (mail-lj1-f172.google.com [209.85.208.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4E27A18C8902 for ; Tue, 22 Oct 2019 10:47:34 +0000 (UTC) Received: by mail-lj1-f172.google.com with SMTP id q78so1512713lje.5 for ; Tue, 22 Oct 2019 03:47:34 -0700 (PDT) Received: from [192.168.1.103] (m83-185-244-38.cust.tele2.se. [83.185.244.38]) by smtp.gmail.com with ESMTPSA id y24sm6567808lfy.20.2019.10.22.03.47.31 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 22 Oct 2019 03:47:31 -0700 (PDT) From: =?UTF-8?Q?Dalebj=c3=b6rk=2c_Tomas?= Message-ID: Date: Tue, 22 Oct 2019 12:47:30 +0200 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="------------1FDFE40FB0C6983501E14F49" Content-Language: sv Subject: [linux-lvm] exposing snapshot block device Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: To: linux-lvm@redhat.com This is a multi-part message in MIME format. --------------1FDFE40FB0C6983501E14F49 Content-Type: text/plain; charset="windows-1252"; format="flowed" Content-Transfer-Encoding: quoted-printable Hi When you create a snapshot of a logical volume. A new virtual dm- device will be created with the content of the changes=20 from the origin. This cow device can than be used to read changed contents etc. In case of an incident, this cow device can be used to read back the=20 changed content to its origin using the "lvmerge" command. The question I have is if there is a way to couple an external cow=20 device to an empty equaly sized logical volume, so that the empty logical volume is aware of that all changed content=20 are placed on this attached cow device? If that is possible, than it will help making instant recovery of LV=20 volumes from an external source using native lvmerge command, from for=20 example a backup server. [EMPTY LOGICAL VOLUME] =EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD ^ =EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD =EF=BF=BD | =EF=BF=BD=EF=BF=BD =EF=BF=BD lvmerge =EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD | [ATTACHED COW DEVICE] Regards Tomas --------------1FDFE40FB0C6983501E14F49 Content-Type: text/html; charset="windows-1252" Content-Transfer-Encoding: quoted-printable

Hi

When you create a snapshot of a logical volume.

A new virtual dm- device will be created with the content of the changes from the origin.

This cow device can than be used to read changed contents etc.


In case of an incident, this cow device can be used to read back the changed content to its origin using the "lvmerge" command.


The question I have is if there is a way to couple an external cow device to an empty equaly sized logical volume,

so that the empty logical volume is aware of that all changed content are placed on this attached cow device?

If that is possible, than it will help making instant recovery of LV volumes from an external source using native lvmerge command, from for example a backup server.


[EMPTY LOGICAL VOLUME]
=EF=BF=BD=EF=BF=BD=EF=BF= =BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD ^
=EF=BF=BD=EF=BF=BD=EF=BF= =BD=EF=BF=BD=EF=BF=BD =EF=BF=BD |
=EF=BF=BD=EF=BF=BD =EF= =BF=BD lvmerge
=EF=BF=BD=EF=BF=BD=EF=BF= =BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD |

[ATTACHED COW DEVICE]

Regards Tomas

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