[linux-lvm] Lvm think provisioning query
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
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!
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