Dne 10. 01. 19 v 14:41 Martin Wilck napsal(a):
On Thu, 2019-01-10 at 12:52 +0100, Zdenek Kabelac wrote:
Dne 10. 01. 19 v 12:40 Martin Wilck napsal(a):
> So far my understanding was that even without zeroing, an LVM
thin
volume could be considered as a drive with "discard zeroes data"
property. If there's a flaw in the argument below, please point it
out
to me.
As said - if you discard 'less then aligned' chunk - nothing happens,
so it cannot be takes as like it would be always zeroing...
Yuck, that's the Catch-22 then. Sorry for having missed that on the
first pass. Wouldn't it be wise to fail discard (or only zeroout?)
requests which aren't chunk-aligned, rather than just doing nothing?
I for one would find it very attractive if dm-thin had a mode
supporting fast zeroout.
I believe '/sys/block/*/queue/discard_zeroes_data is now always returning
false for any device as it's been considered as unreliable logic.
So using 'discard' for zeroing is not really an option here.
Zdenek
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