From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas Gilbert Subject: Re: end to end error recovery musings Date: Mon, 26 Feb 2007 01:01:50 -0500 Message-ID: <45E277CE.3080405@torque.net> References: <45DEF6EF.3020509@emc.com> <45DF80C9.5080606@zytor.com> Reply-To: dougg@torque.net Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <45DF80C9.5080606@zytor.com> Sender: linux-ide-owner@vger.kernel.org To: "H. Peter Anvin" Cc: Ric Wheeler , Linux-ide , linux-scsi , linux-raid@vger.kernel.org, Tejun Heo , James Bottomley , Mark Lord , Neil Brown , Jens Axboe , "Clark, Nathan" , "Singh, Arvinder" , "De Smet, Jochen" , "Farmer, Matt" , linux-fsdevel@vger.kernel.org, "Mizar, Sunita" List-Id: linux-raid.ids H. Peter Anvin wrote: > Ric Wheeler wrote: >> >> We still have the following challenges: >> >> (1) read-ahead often means that we will retry every bad sector at >> least twice from the file system level. The first time, the fs read >> ahead request triggers a speculative read that includes the bad sector >> (triggering the error handling mechanisms) right before the real >> application triggers a read does the same thing. Not sure what the >> answer is here since read-ahead is obviously a huge win in the normal >> case. >> > > Probably the only sane thing to do is to remember the bad sectors and > avoid attempting reading them; that would mean marking "automatic" > versus "explicitly requested" requests to determine whether or not to > filter them against a list of discovered bad blocks. Some disks are doing their own "read-ahead" in the form of a background media scan. Scans are done on request or periodically (e.g. once per day or once per week) and we have tools that can fetch the scan results from a disk (e.g. a list of unreadable sectors). What we don't have is any way to feed such information to a file system that may be impacted. Doug Gilbert