[linux-lvm] Lvm think provisioning query

Gionatan Danti g.danti at assyoma.it
Tue May 3 17:07:36 UTC 2016

Il 03-05-2016 16:49 Zdenek Kabelac ha scritto:
> Now few people (me included) believe  thin volume should error 'ANY'
> further write when there was an overprovisioning error on a device and
> I'm afraid this can't be solved elsewhere then in target driver.
> ATM this thin volume puts filesystem into very complex situation which
> does not have 'winning' scenario in number of cases - so we need to
> define number of policies.
> BUT ATM we clearly communicate - when you run OUT of thin-pool space
> it's serious ADMIN failure - and we could only try to lower damage.
> Thin-pool overfull CANNOT be compared to writing to a full filesystem
> and there is absolutely no guarantee about content of non-flushed 
> files!

True, but non-synched writes should be always treated as "this item can 
be lost if power disappears / system crashes" anyway. On the other 
hands, (f)synched writes should already fail immediately if no space can 
be allocated from the storage subsystem.

In other words, even with a full data pool filesystem intergrity by 
itself should be guaranteed (both by jornaling and fsync), while non 
flushed writes "maybe" (if the data segment required was *already* 
allocated the writes completes, otherwise it fail as an async lost 

For full tmeta things are much worse, as sometime it require 
thin_repair. (ps: if you have two free minutes, please see my other 
email regarding full tmeta. Thanks in advance).

This is my current understanding; please correct me if I am wrong!

Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti at assyoma.it - info at assyoma.it
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