Re: Reserve space for specific thin logical volumes

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Il 13-09-2017 01:31 Zdenek Kabelac ha scritto:
It's not just about 'complexity' in frame work.
You would lose all the speed as well.
You would significantly raise-up  memory requirement.

There is very good reason complex tools like  'thin_ls' are kept in
user-space  outside of kernel   - with  'dm'  we tend to have simpler
kernel logic
and complexity should stay in user-space.

And of course - as pointed out - the size of your 'reserve' is so
vague  :) and could potentially present major portion of you whole
thin-pool size without any extra benefit (as obviously any reserve
could be too small unless you 'reach' fully provisioned state :)

i.e. example:
10G thinLV with 1G chunks - single byte write may require full 1G chunk...
so do you decide to keep 10 free chunks in reserves ??

What was missing (because I thought it was implicit) is that I expect snapshot to never change - ie: they are read-only. Anyway, I was not writing about "resevers" - rather, to preassign/preallocate the required space to a specific volume.
A fallocate on a otherwise thinly provisioned volume, if you like.

Supposedly:

lvmconfig --typeconfig full --withversion

        # Available since version 2.2.89.
        thin_pool_autoextend_threshold=70


However there were some bugs and fixes - and validation for not
allowing to create new thins - so do not try anything below 169 and if
you can
go with 173....


Ah! I was not thinking about thin_pool_autoextend_threshold! I tried with 166 (for now) and I don't see any major problems. However, I will surely upgrade at the first opportunity!

Thanks.

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Danti Gionatan
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