[linux-lvm] about the lying nature of thin

[Chris Friesen]

On 04/29/2016 03:44 AM, Marek Podmaka wrote:

> Now I'm not sure what your use-case for thin pools is.
>
> I don't see it much useful if the presented space is smaller than
> available physical space. In that case I can just use plain LVM with
> PV/VG/LV. For snaphosts you don't care much as if the snapshot
> overfills, it just becomes invalid, but won't influence the original
> LV.

One useful case for "presented space equal to physical space" with thin volumes 
is that it simplifies security issues.

With raw LVM volumes I generally need to zero out the whole volume prior to 
deleting it (to avoid leaking the contents to other users).  This takes time, 
and also seriously hammers the disks when you have multiple volumes being zeroed 
in parallel.

With thin, deletion is essentially instantaneous, and the zeroing penalty is 
paid when the disk block is actually written. Any disk blocks which have not 
been written are simply read as all-zeros.

Chris