Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261582AbVETVRe (ORCPT ); Fri, 20 May 2005 17:17:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261589AbVETVRe (ORCPT ); Fri, 20 May 2005 17:17:34 -0400 Received: from gannon.phys.uwm.edu ([129.89.61.108]:35506 "EHLO gannon.phys.uwm.edu") by vger.kernel.org with ESMTP id S261582AbVETVR2 (ORCPT ); Fri, 20 May 2005 17:17:28 -0400 Date: Fri, 20 May 2005 16:17:27 -0500 (CDT) From: Adam Miller X-X-Sender: amiller@gannon.phys.uwm.edu To: lsorense@csclub.uwaterloo.ca cc: linux-kernel@vger.kernel.org Subject: Re: software RAID (fwd) Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1907 Lines: 46 Here is a response from Bruce Allen. >> If you have a bad sector, it doesn't go away by writing to it again. On >> modern drives, if you see bad sectors the disk is just about dead, and >> will probably be seen as such by the raid system which will then stop >> using the disk entirely and expect you to replace it ASAP. This is false. Modern ATA and SCSI disk drives have several thousand spare sectors. When a sector is unreadable (UNC) which means that the ECC codes are inconsistent, the drive will REALLOCATE the sector, assigning a spare sector the LBA of the failed sector. However it will only do this when you WRITE to the LBA of the failed sector. > The one exception here is if you have a miswritten sector (usually > caused by unexpected power-down), which won't read back correctly - > but running badblocks with one of the 'write-verify' options will > resurrect it. Sectors can have inconsistent ECC codes for a number of reasons: -- failed write during sudden power-down -- damage to magnetic media at this LBA -- other reasons > If you have a drive that has a bad block in it even *after* badblocks has > re-written it, it's time to replace the drive *now*.... Not true. Disks which have reallocated large numbers of blocks are usually failing. But most good disks have some reallocated blocks. > For the original poster: Breaking the mirror and then re-mirroring > from the "good" drive *might* recover the bad block when it re-writes > it. But don't bet on it... It won't 'recover' the bad block. It will write the data (obtained from the good drive) to a newly allocated spare sector on the bad drive. Cheers, Bruce - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/