From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ric Wheeler Subject: Re: [PATCH 003 of 5] md: Change ENOTSUPP to EOPNOTSUPP Date: Fri, 28 Apr 2006 12:48:37 -0400 Message-ID: <44524765.6070703@emc.com> References: <20060428124313.29510.patches@notabene> <1060428025144.30770@suse.de> <62b0912f0604280634x7df2a8a5m9022826876446cb6@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <62b0912f0604280634x7df2a8a5m9022826876446cb6@mail.gmail.com> Sender: linux-raid-owner@vger.kernel.org To: Molle Bestefich Cc: NeilBrown , linux-raid@vger.kernel.org List-Id: linux-raid.ids Molle Bestefich wrote: > NeilBrown wrote: > >> Change ENOTSUPP to EOPNOTSUPP >> Because that is what you get if a BIO_RW_BARRIER isn't supported ! > > > Dumb question, hope someone can answer it :). > > Does this mean that any version of MD up till now won't know that SATA > disks does not support barriers, and therefore won't flush SATA disks > and therefore I need to disable the disks's write cache if I want to > be 100% sure that raid arrays are not corrupted? > > Or am I way off :-). > You are absolutely right - if you do not have a validated, working barrier for your low level devices (or a high end, battery backed array or JBOD), you should disable the write cache on your RAIDed partitions and on your normal file systems ;-) There is working support for SCSI (or libata S-ATA) barrier operations in mainline, but they conflict with queue enable targets which ends up leaving queuing on and disabling the barriers. ric