Date: Thu, 7 Apr 2011 15:02:23 -0700 From: Garrett Cooper <yanegomi@gmail.com> To: Warner Losh <imp@bsdimp.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: <BANLkTikkyjdCbPxO1wvU1KxFuhFLdqbbeg@mail.gmail.com> In-Reply-To: <17BA8DDF-54C9-4E1A-B7DC-A8935B42EC3E@bsdimp.com> References: <201104070817.p378HrHc033571@svn.freebsd.org> <20110407190318.GA97508@freebsd.org> <BANLkTik7Pj5NiEM%2BNeu=neknTxshwcmk-g@mail.gmail.com> <17BA8DDF-54C9-4E1A-B7DC-A8935B42EC3E@bsdimp.com>
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On Thu, Apr 7, 2011 at 2:23 PM, Warner Losh <imp@bsdimp.com> wrote: > > 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> wr= ote: >>> On Thu Apr =A07 11, Alexander Motin wrote: >>>> Author: mav >>>> Date: Thu Apr =A07 08:17:53 2011 >>>> New Revision: 220412 >>>> URL: http://svn.freebsd.org/changeset/base/220412 >>>> >>>> Log: >>>> =A0 Make ada(4) driver to control device write cache, same as ata(4) d= oes. >>>> =A0 Add kern.cam.ada.write_cache sysctl/tunable to control it alike hw= .ata.wc. >>> >>> how hard would it be to support per device sysctls/tunables? i'd really= like to >>> do: >>> >>> kern.cam.ada.0.write_cache=3D0 (root fs) >>> kern.cam.ada.1.write_cache=3D1 (/usr, /var, etc.) >> >> 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. =A0Or any files= ystem that's mounted that you don't really care about the contents of acros= s a power cycle. =A0If you have to recreate it, that's OK. =A0 In those cas= es, you may want the speed increase over safety that write_cache gives you.= =A0Or maybe you have a drive that's doing write caching correctly and one = that doesn't. Alex, Warner: thanks for the practical example; I hadn't really considered that :). Cheers! -Garrett
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