From mboxrd@z Thu Jan 1 00:00:00 1970 From: Can Jeuleers Subject: Re: Migrating a RAID 5 from 4x2TB to 3x6TB ? Date: Tue, 09 Jun 2015 21:18:59 +0200 Message-ID: <55773C23.1010600@gmail.com> References: <167089395.613.1433791723592.JavaMail.zimbra@wieser.fr> <55767860.5000803@gmail.com> <55773493.3050605@youngman.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <55773493.3050605@youngman.org.uk> Sender: linux-raid-owner@vger.kernel.org To: Wols Lists , Pierre Wieser , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 09/06/15 20:46, Wols Lists wrote: > Please expand! Having read the article, it doesn't seem to say anything > more than what is repeated time and time on this list - MAKE SURE YOUR > DRIVES ARE DECENT RAID DRIVES. Large RAID5 arrays are a bad idea because of the probability of unrecoverable read errors occurring during a rebuild, which increases with the size of the array. Decent RAID drives will have better reliability than indecent-ones (haha), but in absolute terms their URE rates are still going to increase with array size. > If you have ERC, then the odd "soft" read error doesn't matter. If you > don't have ERC, then your data is at risk when you replace a drive, and > it doesn't matter how big your drives are, it's the array size that matters. Indeed. Pierre was proposing to further increase the size of his RAID5 array, and I was advising him against it because of the above.