[linux-lvm] Snapshots and disk re-use

[Jonathan Tripathy]

On 23/02/11 16:12, Ray Morris wrote:
> 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,
Thanks for the explanation. But what if I don't want to zero everything? 
I only want to return everything back to the state it was before I 
created the snapshot.