From mboxrd@z Thu Jan 1 00:00:00 1970 From: Giovanni Tessore Subject: Re: Read errors on raid5 ignored, array still clean .. then disaster !! Date: Sat, 30 Jan 2010 23:20:49 +0100 Message-ID: <4B64B0C1.1040503@texsoft.it> References: <4B5F6C73.30707@texsoft.it> <20100127074138.GA9607@maude.comedia.it> <20100129214852.00e565c4@notabene> <4B647E0E.6050609@texsoft.it> <4B64A779.6070809@shiftmail.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4B64A779.6070809@shiftmail.org> Sender: linux-raid-owner@vger.kernel.org To: Asdo Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids > RAID-5 unfortunately is inherently insecure, here is why: > If one drive gets kicked, MD starts recovering to a spare. > At that point any single read error during the regeneration (that's a > scrub) will fail the array. > This is a problem that cannot be overcome in theory. Yes, I was just getting the same conclusion :-( Suppose you have 2Tb mainstream disks, with a read error ratio of 1 sector each 1E+14 bits = 1.25E+13 bytes. It means that you likely get an error every 6.25 times you read the whole disk! So in case of failure of a disk, you have 1 possibility over 6 to fail the array during recostruction. Simply unacceptable! I looked at specs of some enterprise disks, and the read error ratio for them is 1 sector each 1E+15 or each 1E+16. Better but still risky. Ok.. I'll definitely move to raid-6. Also raid-1 with less than 3 disks becomes useless the same way :-( Idem for raid-10 ...wow Well, these two threads on read errors came out as kinda instructive ... doh!! Regards -- Cordiali saluti. Yours faithfully. Giovanni Tessore