From mboxrd@z Thu Jan 1 00:00:00 1970 From: Valdis.Kletnieks@vt.edu Subject: Re: [dm-devel] Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md. Date: Fri, 01 Jun 2007 13:07:07 -0400 Message-ID: <10553.1180717627@turing-police.cc.vt.edu> References: <18006.38689.818186.221707@notabene.brown> <18010.12472.209452.148229@notabene.brown> <20070528094358.GM25091@agk.fab.redhat.com> <5201e28f0705290225v14fdac44hb0382a4137a84d01@mail.gmail.com> <20070529220500.GA6513@agk.fab.redhat.com> <5201e28f0705300212g3be16464u5ee1a4c80db27a11@mail.gmail.com> <465DAC72.1010201@cfl.rr.com> <5201e28f0705310414u1a9aebc4je135748274543946@mail.gmail.com> <465F9197.7060002@gmail.com> <465FC7B1.3060309@gmail.com> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="==_Exmh_1180717627_9513P"; micalg=pgp-sha1; protocol="application/pgp-signature" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Your message of "Fri, 01 Jun 2007 16:16:01 +0900." <465FC7B1.3060309@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Tejun Heo Cc: david@lang.hm, Stefan Bader , Phillip Susi , device-mapper development , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, Jens Axboe , David Chinner , Andreas Dilger , ric@emc.com List-Id: linux-raid.ids --==_Exmh_1180717627_9513P Content-Type: text/plain; charset=us-ascii On Fri, 01 Jun 2007 16:16:01 +0900, Tejun Heo said: > Don't those thingies usually have NV cache or backed by battery such > that ORDERED_DRAIN is enough? Probably *most* do, but do you really want to bet the user's data on it? > The problem is that the interface between the host and a storage device > (ATA or SCSI) is not built to communicate that kind of information > (grouped flush, relaxed ordering...). I think battery backed > ORDERED_DRAIN combined with fine-grained host queue flush would be > pretty good. It doesn't require some fancy new interface which isn't > gonna be used widely anyway and can achieve most of performance gain if > the storage plays it smart. Yes, that would probably be "pretty good". But how do you get the storage device to *reliably* tell the truth about what it actually implements? (Consider the number of devices that downright lie about their implementation of cache flushing....) --==_Exmh_1180717627_9513P Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (GNU/Linux) Comment: Exmh version 2.5 07/13/2001 iD8DBQFGYFI7cC3lWbTT17ARAhCrAKCXsUNK/FKgCgP7h3595UvrISnw+QCg3+P5 1+0QmgTXUfe91UZEeK9GIVE= =BTOx -----END PGP SIGNATURE----- --==_Exmh_1180717627_9513P--