From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Schitter Subject: Re: btrfs csum failed Date: Wed, 04 May 2011 16:42:51 +0200 Message-ID: <4DC165EB.7060304@mur.at> References: <4DC07A10.7070200@mur.at> <20110504002815.GA27861@dhcp231-156.rdu.redhat.com> <4DC0A153.3080806@mur.at> <4DC13B02.9030604@mur.at> <4DC1464D.4060204@mur.at> <000e01cc0a5e$7446eab0$5cd4c010$@nedharvey.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Cc: cwillu , "Fajar A. Nugraha" , linux-btrfs To: Edward Ned Harvey Return-path: In-Reply-To: <000e01cc0a5e$7446eab0$5cd4c010$@nedharvey.com> List-ID: Am 2011-05-04 15:23, schrieb Edward Ned Harvey: >> From: linux-btrfs-owner@vger.kernel.org [mailto:linux-btrfs- >> owner@vger.kernel.org] On Behalf Of Martin Schitter >> >> well -- i am doing a backup of all images every night. this >> process should work like a simple "scrub" because all data (and its >> checksumes) will be read. > > Sorry, not correct. When you read all the data using something in > user-land, the OS only needs to read one side of the data. It can > accelerate by staggering the read requests across multiple disks. So > some sectors remain unread on some disks. > > When you scrub, it reads all the data from all the redundant copies > (mirrored or raid) on all the individual disks in the raid set. ok -- i see -- you're right! i know, there a some befits in the way btrfs and zfs implement RAID / multiply disk usage and checksumming, but i a also want to stay on the save side, when it comes to real practical problems. so i decided to use 'classical' linux software RAID-1 as the base layer. that's a very old fashioned solution, but it usually simply works... and you can change a broken disk without any respect of the used filesystem(s). in general i try to use btrfs only on account of its snapshot features in a very simple way. it looks very strange to me, that i don't see any SMART warnings on the harddisks or errors on other filsystems on the same raid-array. there was also no reboot, power-failure or similar when the corruption suddenly appeared. so i think, a btrfs bug would be the most evident explanation. martin