From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wols Lists Subject: Re: What to do about Offline_Uncorrectable and Pending_Sector in RAID1 Date: Mon, 14 Nov 2016 16:09:12 +0000 Message-ID: <5829E1A8.9060108@youngman.org.uk> References: <942ab8be-cd5c-c6d1-d077-cd295b355c0c@youngman.org.uk> <5828D5DA.1070406@youngman.org.uk> <5829DF1F.7030109@youngman.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Bruce Merry Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 14/11/16 16:03, Bruce Merry wrote: > On 14 November 2016 at 17:58, Wols Lists wrote: >> On 14/11/16 15:52, Bruce Merry wrote: >>> On 13 November 2016 at 23:06, Wols Lists wrote: >>>>> Sounds like that drive could need replacing. I'd get a new drive and do >>>>> that as soon as possible - use the --replace option of mdadm - don't >>>>> fail the old drive and add the new. >>> Would you mind explaining why I should use --replace instead of taking >>> out the suspect drive? I guess I lose redundancy for any writes that >>> occur while the rebuild is happening, but I'd plan to do this with the >>> filesystem unmounted so there wouldn't be any writes. >> >> Because a replace will copy from the old drive to the new, recovering >> any failures from the rest of the array. A fail-and-add will have to >> rebuild the entire new array from what's left of the old, stressing the >> old array much more. > > Okay, I can see how for RAID5 that might be a bad thing. > > In my case however, it sounds like --replace will copy everything from > the failing drive, whereas I'd rather it copied everything from the > good drive. Same stress on the array, less chance of copying dodgy > data. > So long as the data on the drive is correct (it should be) and the drive reports a fault where it can't read it, it'll only copy good data off the bad drive. It'll copy it from the other drive if it's dud. Cheers, Wol