Re: [PATCH] btrfs: raid56: Use correct stolen pages to calculate P/Q

[Christoph Anton Mitterer <calestyo@scientia.net>]

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On Sat, 2016-11-26 at 14:12 +0100, Goffredo Baroncelli wrote:
> I cant agree. If the filesystem is mounted read-only this behavior
> may be correct; bur in others cases I don't see any reason to not
> correct wrong data even in the read case. If your ram is unreliable
> you have big problem anyway.

I'd agree with that - more or less.

If the memory is broken, then even without repairing (on read) a
filesystem that is written to will likely be further corrupted.


I think for safety it's best to repair as early as possible (and thus
on read when a damage is detected), as further  blocks/devices may fail
till eventually a scrub(with repair) would be run manually.

However, there may some workloads under which such auto-repair is
undesirable as it may cost performance and safety may be less important
than that.

Thus I think, there should be a mount-option that let users control
whether repair should happen on normal reads or not... and this should
IMO be independent of whether the fs was mounted ro or rw.
I'd say the default should go for data safety (i.e. repair as soon as
possible).


Cheers,
Chris.

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