[linux-lvm] Snapshots and disk re-use

Ray Morris support at bettercgi.com
Wed Feb 23 16:12:59 UTC 2011

On 23/02/11 14:16, Joe Thornber wrote:
>  And how do I zero just exception store?

In this example, the normal lv is c1_s1.
It has two snapshots, c1_s1_snap0 and c1_s1_snap1.

List the underlying volumes like so:

[root at clonebox2 ~]# ls -1  /dev/mapper/clones-c1_s1*

Half of those would be hidden to lvdisplay, though the man 
page will probably tell you how to show hidden LVs.  "ls"
shows them all.

c1_s1_snap0-cow and c1_s1_snap1-cow are the copy on write 
volumes, the exception stores, I believe.  -real is where 
the current data lives, and c1_s1, the "main" LV is a basically 
a proxy which reads directly from -rela, but diverts writes
so that old data is copied to -cow.  -snap0 is a proxy which 
reads from either -cow or -real as needed.  Hopefully someone 
will tell me where I'm wrong, if I am.

Zeroing c1_s1 first, then c1_s1_snap0-cow would zero everything, 
or zeroing -real and -cow would be more efficient because you 
avoid the copy on write penalty when zeroing the origin. I haven't
actually tested this, only reasoned through it.
Ray Morris
support at bettercgi.com

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On Wed, 23 Feb 2011 14:18:29 +0000
Jonathan Tripathy <jonnyt at abpni.co.uk> wrote:


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> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

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