Date: Tue, 08 Jul 2008 23:10:13 +0200 From: Kris Kennaway <kris@FreeBSD.org> To: Ollivier Robert <roberto@keltia.freenix.fr> Cc: freebsd-fs@freebsd.org Subject: Re: Thinking of using ZFS/FBSD for a backup system Message-ID: <4873D7B5.2060901@FreeBSD.org> In-Reply-To: <20080708204226.GB97977@keltia.freenix.fr> References: <bd9320b30807072315x105cf058tf9f952f0f5bb2a6a@mail.gmail.com> <20080708100701.57031cda@twoflower.in.publishing.hu> <bd9320b30807080131j5e0e02a4y3231d7bfa1738517@mail.gmail.com> <4873C4FA.2020004@FreeBSD.org> <20080708204226.GB97977@keltia.freenix.fr>
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Ollivier Robert wrote: > According to Kris Kennaway: >> (ports-i386:~)> cat /boot/loader.conf >> vfs.zfs.prefetch_disable=1 >> vm.kmem_size=1572864000 > > Hvae you tried w/o the prefetch_disable tunable? I have not done careful measurements, but casual observation suggests that on my workloads I get better performance without prefetch. I have a pair of mirrored disks on an amr, and my workload is quite random-access so prefetching just introduces latencies and wastes already-saturated disk bandwidth. With more disks or a different workload I would expect different performance characteristics. Kris
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