Date: Mon, 22 Jun 2009 08:49:38 +1000 From: Andrew Snow <andrew@modulus.org> To: Dan Naumov <dan.naumov@gmail.com>, freebsd-fs@freebsd.org Subject: Re: ufs2 / softupdates / ZFS / disk write cache Message-ID: <4A3EB902.8080503@modulus.org> In-Reply-To: <cf9b1ee00906211536i37973627ub86948aea63b4156@mail.gmail.com> References: <570433.20373.qm@web37308.mail.mud.yahoo.com> <4A3E9D81.1060406@modulus.org> <cf9b1ee00906211534i76fc8fb4r29b3469af8a2fd7c@mail.gmail.com> <cf9b1ee00906211536i37973627ub86948aea63b4156@mail.gmail.com>
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Dan Naumov wrote: >>> Or: >>> B) use SCSI instead of ATA disks >>> C) use UFS+gjournal instead of UFS+SU >>> D) use ZFS instead of UFS+SU >> All of these solutions still involve disabling of write cache, with a performance hit of varying degrees. (I have tried all of those except gjournal!) B) SCSI drives come with write caching disabled by default. But here, the performance loss is partially made up by Tagged Command Queueing and faster spindle speeds C) gjournal needs to flush the disk cache regularly to maintain consistence. It doesn't need to do it as often but on a write-heavy system it isn't ideal for performance because it flushes everything in the cache and not just the journal. D) ZFS - same as (C) > who on earth is going to accept 2-4 MB/s write speeds from > a modern disk in 2009? eg. remote headless systems which don't do much (DNS server) :-) - Andrew
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