From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Martin K. Petersen" Subject: Re: RFC: detection of silent corruption via ATA long sector reads Date: Sun, 04 Jan 2009 21:43:38 -0500 Message-ID: References: <49580061.9060506@yahoo.com> <87f94c370901021226j40176872h9e5723c6da4afcbe@mail.gmail.com> <495F6622.9010103@anonymous.org.uk> <4960AC15.8030207@anonymous.org.uk> <4960BE63.3040608@anonymous.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: In-Reply-To: <4960BE63.3040608@anonymous.org.uk> (John Robinson's message of "Sun\, 04 Jan 2009 13\:49\:23 +0000") Sender: linux-raid-owner@vger.kernel.org To: John Robinson Cc: "Martin K. Petersen" , linux-raid@vger.kernel.org List-Id: linux-raid.ids >>>>> "John" == John Robinson writes: John> I've thought about this again, and I'm wrong; there may be John> complications in handling the cookies up and down the stack where John> more than one layer thinks it knows how to have another go, but I John> can see what you describe as being useful and relatively John> device-agnostic. Yeah, care will need to be taken if you have multiple layers in the stack providing redundancy. That's usually not the case, though. John> I wonder if there might also be scope for cookies going down John> through the stack to carry an indication of how hard to try; some John> filesystems or other consumers of block devices may be willing to John> ask again or want to be told about problems quickly (e.g. btrfs John> over RAID over TLER-equipped discs), while some may need best John> efforts all out first time because they can't cope will failure John> returns (e.g. FAT over cheap IDE discs). We already have this functionality. It's orthogonal to the integrity bits. You can tell the low-level drivers either fail a request immediately or to retry. That's only a software thing, though. It doesn't work terribly well with consumer harddrives that assume there's only one copy of the data and consequently enter annoying-click-mode and retry for a long time. Nearline and enterprise drives assume there's a redundant copy and will not try as hard under the assumption that you know how to remedy the problem. -- Martin K. Petersen Oracle Linux Engineering