From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Turmel Subject: Re: mdadm --create parameter ordering Date: Mon, 13 Jul 2015 09:17:52 -0400 Message-ID: <55A3BA80.50505@turmel.org> References: <20150713105928.GA19366@cthulhu.home.robinhill.me.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150713105928.GA19366@cthulhu.home.robinhill.me.uk> Sender: linux-raid-owner@vger.kernel.org To: Steven Reddie , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 07/13/2015 06:59 AM, Robin Hill wrote: [snip /] Let me elaborate on one of Robin's comments: > The --assume-clean option will prevent parity calculation (as it assumes > that the parity on disk is already correct), which may be what you're > after. It should only be used it you're absolutely certain of the data > though, as it can lead to large-scale corruption otherwise. It is not enough to be certain of the order to use --create --assume-clean on existing data. You must also be certain of superblock type, chunk size, data offset, and layout option. Data loss due to unwise use of --create has a history of bad outcomes. It destroys the previous metadata on array members, metadata that is almost always needed to recover damaged arrays. The --create option should *never* be used on an array with important data without first asking for advice on this list. Phil