From mboxrd@z Thu Jan 1 00:00:00 1970 From: Aryeh Leib Taurog Subject: Re: Reassembling RAID1 after good drive was offline [newbie] Date: Sun, 4 Jan 2015 12:20:09 +0200 Message-ID: <20150104102009.GA4511@deb76.aryehleib.com> References: <54A6E5B1.2090602@tigertech.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <54A6E5B1.2090602@tigertech.com> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On Fri, Jan 02, 2015 at 6:38 PM, Robert L Mathews wrote: > Your question is about how to reassemble them without a resync, > which is understandable, but the reason md isn't doing that > automatically is that it thinks they might be different. > I personally would always do a resync in such a case. A flaky cable > suggests that data on it is suspect, and this is one of the things > RAID 1 is for: it allows you to copy clean data to suspect > partitions. > But I'm known to be data-paranoid. Other people may have different > opinions/suggestions. Thanks. I tend to agree. Would the resync just copy all the data from the "good" drive back to the "failed" drive? For diagnostic purposes, it would actually be a lot more informative to compare the two drives and see if there really is data corruption on one of them or not. Is there a way to do that? If I were to demonstrate that the data are in sync, I would want to reassemble without resync. Also, in my situation, since for now I'm just using a pair of external drives, I could easily imagine accidentally trying to assemble the array when one of the drives is powered down. Then this situation would arise again without faulty hardware. I suppose an 'assemble' script could help protect against the latter case by checking first that both devices are available. Prudence notwithstanding, I do think there are valid cases for reassembling this array without resync. If there's a way to do that, I'd still like to know. With appreciation, Aryeh Leib Taurog