From owner-freebsd-fs@FreeBSD.ORG Mon Jun 22 12:44:37 2009 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 306C71065675 for ; Mon, 22 Jun 2009 12:44:37 +0000 (UTC) (envelope-from numisemis@yahoo.com) Received: from web37305.mail.mud.yahoo.com (web37305.mail.mud.yahoo.com [209.191.90.248]) by mx1.freebsd.org (Postfix) with SMTP id E1F9D8FC13 for ; Mon, 22 Jun 2009 12:44:36 +0000 (UTC) (envelope-from numisemis@yahoo.com) Received: (qmail 69468 invoked by uid 60001); 22 Jun 2009 12:44:36 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s1024; t=1245674676; bh=chNWlw/RHA6ZKqx0ZNHE3Gbs835BhISNi3NYoB5a858=; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:Cc:In-Reply-To:MIME-Version:Content-Type; b=5DrFGIkB73YgnWnbe2BUImG4O66r5rzw35SDyzyYe45exfWSefpSLMGi076+5CDXSzDkMoROVikz2bWhOOThQv9N3FpQKZbKU3EZ76K9cCvp4B68694H7NctMlsypTBrXvyT9xC97DMfRuJYoz/z9uuSbi+xCT4mX9k7dhEEqeM= DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:Cc:In-Reply-To:MIME-Version:Content-Type; b=2nrosbDw20rAXDYOtWoDDOuUkqfOJRnrWCNjT7z+HzaNnod4prmzWwZH7jSOsL4/PdtVNlYPC/ef3F9z4FX8GuoWqIjOoX0vYOrkJSgawg5S3QTeAKr8tC3bUzlNnPmj82vKEGStCIxLb7+C/cNASLuQkErdIIUZVL3pdtwGM9Q=; Message-ID: <457065.69200.qm@web37305.mail.mud.yahoo.com> X-YMail-OSG: KDjwnkkVM1kSWC0DwOtm5jACjtBWy0q9F8IVB6tWnnsAfbVOFAdaj8P0YIZMjFGOKKdUQuUd9QcD7MNhNazNcjNoO16saLEUOi8oTC6zk63vS1gP8LtaF_CkGlgPwlw_67T__nDZrJa8Gh0PoYJqZdDkBW1Tlr6iB6ofEC6F1dpbcJBIOfy_Zv9Ncav2Rn_OuYS51CkDd.LNPKHVx_1CCpeLxiDopQGENXECNy6RXr0Y8eJgHT5KA3L.C6JPiRbvCcrRZR2h7rvqSXUqORWZx6FU1zu0ROSDsNKfO1ZwAea5sk_FU9WKDDeKssdKHSxU40SE2A-- Received: from [87.252.131.19] by web37305.mail.mud.yahoo.com via HTTP; Mon, 22 Jun 2009 05:44:36 PDT X-Mailer: YahooMailRC/1277.43 YahooMailWebService/0.7.289.15 References: <570433.20373.qm@web37308.mail.mud.yahoo.com> <4A3E9D81.1060406@modulus.org> <4A3EB902.8080503@modulus.org> Date: Mon, 22 Jun 2009 05:44:36 -0700 (PDT) From: Simun Mikecin To: Andrew Snow In-Reply-To: <4A3EB902.8080503@modulus.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: freebsd-fs@freebsd.org Subject: Re: ufs2 / softupdates / ZFS / disk write cache X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 22 Jun 2009 12:44:37 -0000 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.