[linux-lvm] Reserve space for specific thin logical volumes

[Zdenek Kabelac]

Dne 10.9.2017 v 00:04 Gionatan Danti napsal(a):
> Il 08-09-2017 12:35 Gionatan Danti ha scritto:
>> Hi list,
>> as by the subject: is it possible to reserve space for specific thin
>> logical volumes?
>>
>> This can be useful to "protect" critical volumes from having their
>> space "eaten" by other, potentially misconfigured, thin volumes.
>>
>> Another, somewhat more convoluted, use case is to prevent snapshot
>> creation when thin pool space is too low, causing the pool to fill up
>> completely (with all the associated dramas for the other thin
>> volumes).
>>
>> Thanks.
> 
> Hi all,
> anyone with some informations?
> 
> Any comment would be very appreciated :)
> Thanks.


Hi


Not sure for which information are you looking for ??

Having 'reserved' space for thinLV - means - you have to add more space
to this thin-pool -  there is not much point in keeping space in VG,
which could be only used for extension of particular LV ??

What we do have thought is 'shard' "_pmspare' extra space for metadata 
recovery, but there is nothing  like that for data space (and not even planned).

There is support for so-called- fully-provisioned thinLVs withing thin-pool 
in-plan, but that probably doesn't suit your needs.


The first question here is - why do you want to use thin-provisioning ?

As thin-provisioning is about 'promising the space you can deliver later when 
needed'  - it's not about hidden magic to make the space out-of-nowhere.
The idea of planning to operate thin-pool on 100% fullness boundary is simply 
not going to work well - it's  not been designed for that use-case - so if 
that's been your plan - you will need to seek for other solution.
(Unless you seek for those 100% provisioned devices)

Regards


Zdenek