[linux-lvm] Why use thin_pool_autoextend_threshold < 100 ?

[Zdenek Kabelac]

Dne 31.7.2018 v 04:44 Marc MERLIN napsal(a):
> On Fri, Jul 27, 2018 at 11:26:58AM -0700, Marc MERLIN wrote:
>> Hi Zdenek,
>>
>> Thanks for your helpful reply.
>   
> Ha again Zdenek,
> 
> Just to confirm, am I going to be ok enough with the scheme I described
> as long as I ensure that 'Allocated pool data' does not get to 100% ?
> 
> For now, I have my btrfs filesystems mounted with "discard", so
> hopefully it should tell dm-thin when it can free up/reuse blocks.
> 
> Given that, am I more or less ok using dm-thin that way?
> 
> And for my own understanding, is there any reason why I would even want
> to consider thin_pool_autoextend_threshold < 100 ?
> 

Hi

If you monitor amount of free space for data AND for metadata in thin-pool
yourself you can keep easily threshold == 100.

Just don't forget when you upsize 'data' - you should also typically
extend also metadata -  it's not uncommon issue user  start with small
'data' & 'metadata' LV with thin-pool - then  continue to only extend
thin-pool 'data' volume and ignore/forget about metadata completely
and hit the full metadata device - which can lead to many troubles
(hitting full dataLV is normally not a big deal).

Regards

Zdenek