[linux-lvm] Thin metadata volume bigger than 16GB ?

[Gionatan Danti <g.danti@assyoma.it>]

Hi list,
I wonder if a method exists to have a >16 GB thin metadata volume.

When using a 64 KB chunksize, a maximum of ~16 TB can be addressed in a 
single thin pool. The obvious solution is to increase the chunk size, as 
128 KB chunks are good for over 30 TB, and so on. However, increasing 
chunksize is detrimental for efficiency/performance when heavily using 
snapshot.

Another simple and very effective solution is to have multiple thin 
pools, ie: 2x 16 GB metadata volumes with 64 KB chunksize is good, 
again, for over 30 TB thin pool space.

That said, the naive but straightforward would be to increase maximum 
thin pool size. So I have some questions:

- is the 16 GB limit an hard one?
- there are practical consideration to avoid that (eg: slow thin_check 
for very bug metadata volumes)?
- if so, why I can not find any similar limit (in the docs) for cache 
metadata volumes?
- what is the right thing to do when a 16 GB metadata volume fill-up, if 
it can not be expanded?

Thanks.

-- 
Danti Gionatan
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