Date: Sun, 3 Mar 2013 19:01:27 -0800 (PST) From: Don Lewis <truckman@FreeBSD.org> To: phk@phk.freebsd.dk Cc: deeptech71@gmail.com, freebsd-current@FreeBSD.org, peter@rulingia.com, ian@FreeBSD.org Subject: Re: access to hard drives is "blocked" by writes to a flash drive Message-ID: <201303040301.r2431Rjm008175@gw.catspoiler.org> In-Reply-To: <52867.1362317749@critter.freebsd.dk>
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On 3 Mar, Poul-Henning Kamp wrote: > For various reasons (see: Lemming-syncer) FreeBSD will block all I/O > traffic to other disks too, when these pileups gets too bad. The Lemming-syncer problem should have mostly been fixed by 231160 in head (231952 in stable/9 and 231967 in stable/8) a little over a year ago. The exceptions are atime updates, mmaped files with dirty pages, and quotas. Under certain workloads I still notice periodic bursts of seek noise. After thinking about it for a bit, I suspect that it could be atime updates, but I haven't tried to confirm that. When using TCQ or NCQ, perhaps we should limit the number of outstanding writes per device to leave some slots open for reads. We should probably also prioritize reads over writes unless we are under memory pressure.
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