Date: Thu, 7 Apr 2011 15:23:31 -0600 From: Warner Losh <imp@bsdimp.com> To: Garrett Cooper <yanegomi@gmail.com> Cc: svn-src-head@freebsd.org, Alexander Best <arundel@freebsd.org>, Alexander Motin <mav@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org Subject: Re: svn commit: r220412 - in head: share/man/man4 sys/cam/ata Message-ID: <17BA8DDF-54C9-4E1A-B7DC-A8935B42EC3E@bsdimp.com> In-Reply-To: <BANLkTik7Pj5NiEM%2BNeu=neknTxshwcmk-g@mail.gmail.com> References: <201104070817.p378HrHc033571@svn.freebsd.org> <20110407190318.GA97508@freebsd.org> <BANLkTik7Pj5NiEM%2BNeu=neknTxshwcmk-g@mail.gmail.com>
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On Apr 7, 2011, at 3:00 PM, Garrett Cooper wrote: > On Thu, Apr 7, 2011 at 12:03 PM, Alexander Best <arundel@freebsd.org> = wrote: >> On Thu Apr 7 11, Alexander Motin wrote: >>> Author: mav >>> Date: Thu Apr 7 08:17:53 2011 >>> New Revision: 220412 >>> URL: http://svn.freebsd.org/changeset/base/220412 >>>=20 >>> Log: >>> Make ada(4) driver to control device write cache, same as ata(4) = does. >>> Add kern.cam.ada.write_cache sysctl/tunable to control it alike = hw.ata.wc. >>=20 >> how hard would it be to support per device sysctls/tunables? i'd = really like to >> do: >>=20 >> kern.cam.ada.0.write_cache=3D0 (root fs) >> kern.cam.ada.1.write_cache=3D1 (/usr, /var, etc.) >=20 > Does it really make sense to turn on write caching for one drive and > not the other(s)? Think about /usr/obj or /tmp and ask that question again. Or any = filesystem that's mounted that you don't really care about the contents = of across a power cycle. If you have to recreate it, that's OK. In = those cases, you may want the speed increase over safety that = write_cache gives you. Or maybe you have a drive that's doing write = caching correctly and one that doesn't. Warner
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