'[linux-lvm] Derivative snapshots'

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List:       linux-lvm
Subject:    [linux-lvm] Derivative snapshots
From:       Mike Young <myoung () wildernessvoice ! com>
Date:       2011-03-24 15:22:04
Message-ID: 66707497-76A4-4BA2-835A-791E6D3F0924 () wildernessvoice ! com
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Hi,

I'd like to say in advance that I really appreciate any guidance/help I =
can receive with this request.

I am looking for a way to perform a derivative snapshot (i.e., a =
snapshot of an existing snapshot volume). I understand that there can be =
issues with respect to restoring an Original volume from such a =
derivative, and I'd like to say that I have no intention of any such =
restoration.

Basically, I want to use lvm to quickly generate a 100% block replica of =
an existing LV.

For example:
To create first snapshot
 lvcreate -L[same size as original] -sn [snapshot_1] /dev/[path to =
original]

After some time, I make a number of changes to the snapshot volume and I =
wish to replicate off of that.
lvcreate -L[same size as snapshot_1] -sn [snapshot_2] /dev/[path to =
snapshot_1]

When I try to create the derivative snapshot, I get the message =
"Snapshots of snapshots are not supported yet."

I can see how lvcreate validates the various arguments, but I'm not =
immediately seeing how this particular check is performed where it looks =
at the "type" of the source volume.

Can someone help me with where this check is actually performed?

Thanks,

Mike=

[Attachment #5 (unknown)]

<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; \
-webkit-line-break: after-white-space; ">Hi,<div><br></div><div>I'd like to say in \
advance that I really appreciate any guidance/help I can receive with this \
request.</div><div><br></div><div>I am looking for a way to perform a derivative \
snapshot (i.e., a snapshot of an existing snapshot volume). I understand that there \
can be issues with respect to restoring an Original volume from such a derivative, \
and I'd like to say that I have no intention of any such \
restoration.</div><div><br></div><div>Basically, I want to use lvm to quickly \
generate a 100% block replica of an existing LV.</div><blockquote \
class="webkit-indent-blockquote" style="margin: 0 0 0 40px; border: none; padding: \
0px;"><div><br></div></blockquote>For example:<br><blockquote \
class="webkit-indent-blockquote" style="margin: 0 0 0 40px; border: none; padding: \
0px;"><div><b>To create first snapshot</b></div><div>&nbsp;lvcreate -L[same size as \
original] -sn [snapshot_1] /dev/[path to original]</div><div><br></div><div>After \
some time, I make a number of changes to the snapshot volume and I wish to replicate \
off of that.</div><div>lvcreate -L[same size as snapshot_1] -sn [snapshot_2] \
/dev/[path to snapshot_1]</div><div><br></div><div>When I try to create the \
derivative snapshot, I get the message "Snapshots of snapshots are not supported \
yet."</div></blockquote><div><br></div><div>I can see how lvcreate validates the \
various arguments, but I'm not immediately seeing how this particular check is \
performed where it looks at the "type" of the source \
volume.</div><div><br></div><div>Can someone help me with where this check is \
actually performed?</div><div><br></div><div>Thanks,</div><div><br></div><div>Mike</div></body></html>

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