From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bartlomiej Zolnierkiewicz Subject: Re: [RFC/PATCH 0/7] enable honoring write cache setting of IDE drive Date: Fri, 28 Jan 2005 23:32:53 +0100 Message-ID: <58cb370e050128143221c7cac8@mail.gmail.com> References: <58cb370e0501281349543d0d14@mail.gmail.com> <200501282215.j0SMFegK022818@falcon10.austin.ibm.com> Reply-To: Bartlomiej Zolnierkiewicz Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from wproxy.gmail.com ([64.233.184.198]:24139 "EHLO wproxy.gmail.com") by vger.kernel.org with ESMTP id S262798AbVA1WdR (ORCPT ); Fri, 28 Jan 2005 17:33:17 -0500 Received: by wproxy.gmail.com with SMTP id 67so324449wri for ; Fri, 28 Jan 2005 14:33:17 -0800 (PST) In-Reply-To: <200501282215.j0SMFegK022818@falcon10.austin.ibm.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Doug Maxey Cc: Jens Axboe , Jeff Garzik , Linux IDE Mailing List On Fri, 28 Jan 2005 16:15:40 -0600, Doug Maxey wrote: > > On Fri, 28 Jan 2005 22:49:08 +0100, Bartlomiej Zolnierkiewicz wrote: > >On Fri, 28 Jan 2005 15:43:52 -0600, Doug Maxey wrote: > >> > >> On Fri, 28 Jan 2005 22:35:17 +0100, Bartlomiej Zolnierkiewicz wrote: > >> >On Fri, 28 Jan 2005 15:06:22 -0600, Doug Maxey wrote: > >> >> > >> >> On Fri, 28 Jan 2005 20:11:37 +0100, Bartlomiej Zolnierkiewicz wrote: > >> >> >On Fri, 28 Jan 2005 12:16:01 -0600, Doug Maxey wrote: > >> >> > > >> >> >We have too many config options already. > >> >> > > >> >> >Behavior should be simple: > >> >> >* no cache flushes - wcache off by default > >> >> >* cache flushes - wcache on by default > >> >> >* inform user about the wcache status > >> >> >* allow changing of wcache by user > >> >> > >> >> My interpretation of what you are saying here is the selection of > >> >> "cache flush" drives the setting of wcache. Are you saying that > >> >> "barrier=off" on the boot line the currently (only and will remain) > >> >> supported method controlling flushes? > >> > > >> >No, I am saying that cache flush is a property of disk not fs. > >> >On the contrary barrier is a property of filesystem. > >> > >> Ok. We are talking apples and oranges here. The disk DOES have FLUSH CACHE, > >> which is the main reason these drives work in the later kernels. You can > >> switch wcache back and forth, provided that the correct flushing is done. > >> > >> Write cache, on the otherhand, which is disabled on the drive by default, > >> is not honored. > > > >What is the practical reason to honor it? > > The datacenters/server folks that would be using these drives would > expect them to remain as set. I have to check, but unless something > has changed very recently in the kernel, setting with hdparm does not > "stick" in the sense that the command succeeds to the disk, but no change > is made to the barrier. It is not a problem for IDE driver (flushes become no-ops) and this way you can later enable wcache and still use barries. > here is the current scenario with a drive that can work with wcache off. > - idedisk_setup() forces enabled wcache. > - enabled wcache uses FLUSH. > - hdparm -W0 disables cache without matching change to barriers. > > - Setting "barrier=off" has the undesired side effect of not flushing > with wcache enabled on the drive. Some people with certain servers are > _ssooo_ picky. :) This is fs layer problem.