From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from resqmta-po-05v.sys.comcast.net ([96.114.154.164]:52693 "EHLO resqmta-po-05v.sys.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752053AbbJTVCt (ORCPT ); Tue, 20 Oct 2015 17:02:49 -0400 Date: Tue, 20 Oct 2015 15:54:38 -0500 From: Tim Walberg To: Austin S Hemmelgarn Cc: Duncan <1i5t5.duncan@cox.net>, linux-btrfs@vger.kernel.org Subject: Re: Expected behavior of bad sectors on one drive in a RAID1 Message-ID: <20151020205438.GC4598@comcast.net> Reply-To: Tim Walberg References: <201510201545.50705.russell@coker.com.au> <56263B0B.4050502@gmail.com> <201510210015.54337.russell@coker.com.au> <562648B5.2020401@gmail.com> <56269D1C.5080006@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <56269D1C.5080006@gmail.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 10/20/2015 15:59 -0400, Austin S Hemmelgarn wrote: >> ......... >> With a 32-bit checksum and a 4k block (the math is easier with >> smaller numbers), that's 4128 bits, which means that a random >> single bit error will have a approximately 0.24% chance of >> occurring in a given bit, which translates to an approximately >> 7.75% chance that it will occur in one of the checksum bits. For a >> 16k block it's smaller of course (around 1.8% I think, but that's >> just a guess), but it's still sufficiently statistically likely >> that it should be considered. >> ......... Last I checked, a 4 kilo-BYTE block consisted of 32768 BITs... So the percentages should in fact be considerably smaller than that. -- twalberg@gmail.com