Date: Mon, 22 Jun 2009 05:44:36 -0700 (PDT) From: Simun Mikecin <numisemis@yahoo.com> To: Andrew Snow <andrew@modulus.org> Cc: freebsd-fs@freebsd.org Subject: Re: ufs2 / softupdates / ZFS / disk write cache Message-ID: <457065.69200.qm@web37305.mail.mud.yahoo.com> In-Reply-To: <4A3EB902.8080503@modulus.org> References: <570433.20373.qm@web37308.mail.mud.yahoo.com> <4A3E9D81.1060406@modulus.org> <cf9b1ee00906211534i76fc8fb4r29b3469af8a2fd7c@mail.gmail.com> <cf9b1ee00906211536i37973627ub86948aea63b4156@mail.gmail.com> <4A3EB902.8080503@modulus.org>
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Andrew Snow wrote:
> 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
SCSI drives get configured by the controller BIOS and/or kernel driver. It usually means that both TCQ and write cache become enabled. It is considered safe to enable write cache if TCQ is enabled.
The same would be valid for SATA with NCQ enabled. But FreeBSD does not (yet) support SATA NCQ.
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