[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*
/dev/mapper/clones-c1_s1
/dev/mapper/clones-c1_s1-real
/dev/mapper/clones-c1_s1_snap0
/dev/mapper/clones-c1_s1_snap0-cow
/dev/mapper/clones-c1_s1_snap1
/dev/mapper/clones-c1_s1_snap1-cow
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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> linux-lvm at redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>
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