From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eyal Lebedinsky Subject: Re: mismatch_cnt questions Date: Mon, 05 Mar 2007 08:21:43 +1100 Message-ID: <45EB3867.8050907@eyal.emu.id.au> References: <17898.45673.573800.56474@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <17898.45673.573800.56474@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: Christian Pernegger , linux-raid@vger.kernel.org List-Id: linux-raid.ids Neil Brown wrote: > On Sunday March 4, pernegger@gmail.com wrote: >>I have a mismatch_cnt of 384 on a 2-way mirror. [trim] >>3) Is the "repair" sync action safe to use on the above kernel? Any >>other methods / additional steps for fixing this? > > "repair" is safe, though it may not be effective. > "repair" for raid1 was did not work until Jan 26th this year. > Before then it was identical in effect to 'check'. How is "repair" safe but not effective? When it finds a mismatch, how does it know which part is correct and which should be fixed (which copy of raid1, or which block in raid5)? When a disk fails we know what to rewrite, but when we discover a mismatch we do not have this knowledge. It may corrupt the good copy of a raid1. -- Eyal Lebedinsky (eyal@eyal.emu.id.au)