Date: Wed, 21 Apr 2004 12:05:56 -0500 From: "Jim C. Nasby" <jim@nasby.net> To: Uwe Doering <gemini@geminix.org> Cc: freebsd-performance@freebsd.org Subject: Re: vfs.hirunningspace on a 3ware 8506 Message-ID: <20040421170556.GB41429@nasby.net> In-Reply-To: <4085AA4B.1020700@geminix.org> References: <20040420195010.GZ87362@nasby.net> <4085869E.7090306@he.iki.fi> <4085AA4B.1020700@geminix.org>
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On Wed, Apr 21, 2004 at 12:55:07AM +0200, Uwe Doering wrote: > Petri Helenius wrote: > >Jim C. Nasby wrote: > > > >>Has anyone done any testing to see what value of vfs.hirunningspace is > >>optimal for a 3ware 8506-8? > >> > >Do the 3ware controllers actually care about this value due to the > >onboard processing and cache? I thought all writes are satisfied > >immediately? > > The controller itself doesn't care, but the kernel does. With the > current implementation, the amount of memory associated with outstanding > read requests is subtracted from vfs.hirunningspace. With many > concurrent read requests there is no reserve left for write operations, > so write performance can suffer substantially. > > This balancing effect is actually intended in order to give read > requests some priority, but in high performance systems with fast, > caching raid controllers the default value of said variable is too low > and therefore poses a bottleneck. Unfortunately, it seems the 8500 series only has 1.8MB of cache, so it seems like the out-of-the-box setting of 1M may not be too far off. Is it normally advisable to set vfs.hirunningspace = whatever the controller's cache is? -- Jim C. Nasby, Database Consultant jim@nasby.net Member: Triangle Fraternity, Sports Car Club of America Give your computer some brain candy! www.distributed.net Team #1828 Windows: "Where do you want to go today?" Linux: "Where do you want to go tomorrow?" FreeBSD: "Are you guys coming, or what?"
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