From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from eastrmfepo102.cox.net ([68.230.241.214]:41863 "EHLO eastrmfepo102.cox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751834AbaJIMmd (ORCPT ); Thu, 9 Oct 2014 08:42:33 -0400 Received: from eastrmimpo210 ([68.230.241.225]) by eastrmfepo102.cox.net (InterMail vM.8.01.05.15 201-2260-151-145-20131218) with ESMTP id <20141009124232.KMML24978.eastrmfepo102.cox.net@eastrmimpo210> for ; Thu, 9 Oct 2014 08:42:32 -0400 Date: Thu, 9 Oct 2014 05:42:31 -0700 From: Duncan <1i5t5.duncan@cox.net> To: Hugo Mills Cc: linux-btrfs@vger.kernel.org Subject: Re: What is the vision for btrfs fs repair? Message-ID: <20141009054231.7f28f7d5@ws> In-Reply-To: <0zvr1p0162Q6ekd01zvtN0> References: <54358C77.2070808@redhat.com> <54367193.6000202@gmail.com> <0zvr1p0162Q6ekd01zvtN0> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Thu, 9 Oct 2014 12:55:50 +0100 Hugo Mills wrote: > On Thu, Oct 09, 2014 at 11:53:23AM +0000, Duncan wrote: > > Austin S Hemmelgarn posted on Thu, 09 Oct 2014 07:29:23 -0400 as > > excerpted: > > > > > Also, you should be running btrfs scrub regularly to correct > > > bit-rot and force remapping of blocks with read errors. While > > > BTRFS technically handles both transparently on reads, it only > > > corrects thing on disk when you do a scrub. > > > > AFAIK that isn't quite correct. Currently, the number of copies is > > limited to two, meaning if one of the two is bad, there's a 50% > > chance of btrfs reading the good one on first try. > > Scrub checks both copies, though. It's ordinary reads that don't. While I believe I was clear in full context (see below), agreed. I was talking about normal reads in the above, not scrub, as the full quote should make clear. I guess I could have made it clearer in the immediate context, however. Thanks. > > Thus, while btrfs may randomly bump into a bad block and rewrite it > > with the good copy, scrub is the only way to systematically detect > > and (if there's a good copy) fix these checksum errors. -- Duncan - No HTML messages please, as they are filtered as spam. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman