Very inconsistent (read) speed on UFS2
lev at FreeBSD.org
Wed Aug 31 08:11:06 UTC 2011
You wrote 31 августа 2011 г., 3:00:45:
> So, my new theory on why your O_DIRECT test is running slowly is due
> to the single threading in the GEOM layer. Pawel Jakub Dawidek (pjd@)
> gave a very interesting talk on this problem at this year's BSDCan.
I want to stress my point: it is not low speed, what especially
bother me. It is inconsistency.
Bad drive, always-single-threaded-GEOM, etc., should give consistent
Bad code in geom_raid5 could give inconsistent write speed, du to
caching, but reading path is as straight and simple as possible here.
Bad drive or AST-GEOM is not what simple to fix (ok, bad drive IS
simple to replace, of course). But I suspect, that here is some simple
"misunderstanding" between geom_raid5 code and VFS/FFS2 layer, which I
could fix. But I don't know where to look at.
// Black Lion AKA Lev Serebryakov <lev at FreeBSD.org>
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