Date: Fri, 20 Feb 2015 16:29:26 +0300 From: Ilya A. Arkhipov <rum1cro@yandex.ru> To: "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org> Subject: Re: Disable zfs prefetch by default Message-ID: <614751424438966@web18h.yandex.ru> In-Reply-To: <66c5011b.0fcc09f9@fabiankeil.de> References: <54E71E20.8080303@yandex.ru> <66c5011b.0fcc09f9@fabiankeil.de>
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20.02.2015, 15:52, "Fabian Keil" <freebsd-listen@fabiankeil.de>: > "Ilya A. Arkhipov" <rum1cro@yandex.ru> wrote: >> šWe have zfs prefetch enabled by default with > 4GB, but I didn't seen >> šany case for using it, and all tuning guide saying to disable it. > > Which tuning guides are you referring to? This one https://wiki.freebsd.org/ZFSTuningGuide >> šMaybe we disable zfs prefetch by default ? Or could you please provide >> šwhy it needed. > > Whether or not prefetching is useful depends on the workload > and the setup. > > If you doubt that the prefetch default is useful for your workload > (for example because your systems mainly do small "random" reads > from "random" files), you can easily test this by disabling prefetching > for a while. > > If this is too much work (or if no difference can be measured), > the default is probably fine. > > Fabian Actualy on all my servers(more 300 ^_^), I've disable prefetch because on all have the same issue: http://i.imgur.com/aJNCiBK.png http://i.imgur.com/Di3FuWw.png http://i.imgur.com/uunH1k8.png http://i.imgur.com/vjYiB2K.png -- With Best Regards, Ilya A. Arkhipov
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