[linux-lvm] Snapshots and disk re-use

[Jonathan Tripathy]

On 05/04/2011 21:59, James Hawtin wrote:
> On 05/04/2011 20:48, Jonathan Tripathy wrote:
>>
>> Yeah, I'll have to try this on a non-production server. Which kernel 
>> do you expect to crash? The Dom0 (Xen + LVM host) or the VM? Anyway, 
>> just thinking about it, it seems that pausing/saving/shutting down 
>> the VM is a must, as the VM may be writing to disk at the time of 
>> zeroing the cow (!!).
>>
>> In the hosting industy, what does everyone else do? Do they just 
>> ignore the issue???
>>
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>>
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>
> As an alturnative could you not?
>
> 1) Create snapshot lv using specific physical extents.
> lvcreate -s -l 100 ..... /dev/sdx1:0-99
> 2) Backup VM
> 3) Delete snapshot lv
> 4) create a normal lv using same physical extents
> lvcreate -l 100 ..... /dev/sdx1:0-99
> 5) zero normal lv
> 6) delete normal lv
>
> James 
Hi James,

Interesting, didn't know you could do that! However, how do I know that 
the PEs aren't being used by LVs? Also, could you please explain the 
syntax? Normally to create a snapshot, I would do:

lvcreate -L20G -s -n backup /dev/vg0/customerID

Thanks

Thanks