From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from twilight.int.mornfall.net (ovpn-112-27.phx2.redhat.com [10.3.112.27]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id o97CEtWR029609 for ; Thu, 7 Oct 2010 08:14:56 -0400 From: Petr Rockai References: <87363.97197.qm@web120701.mail.ne1.yahoo.com> <4CAB46FE.9050309@cfl.rr.com> <86106.13599.qm@web120714.mail.ne1.yahoo.com> <87ocb7jk3d.fsf@twilight.int.mornfall.net.> <4CACC6B0.2030603@cfl.rr.com> Date: Thu, 07 Oct 2010 14:14:43 +0200 In-Reply-To: <4CACC6B0.2030603@cfl.rr.com> (Phillip Susi's message of "Wed, 6 Oct 2010 14:57:52 -0400") Message-ID: <87fwwijj2k.fsf@twilight.int.mornfall.net.> MIME-Version: 1.0 Subject: Re: [linux-lvm] LVM mirror questions Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Phillip Susi Cc: LVM general discussion and development Phillip Susi writes: >> LVM has a generation counter as well. It's only updated on metadata >> writes though, so it doesn't cost anything. (Log is not part of metadata >> in this sense.) When you lose a leg (and use dmeventd), the metadata on >> the remaining PVs is updated to say that. The leg is also yanked from >> the mirror. You can add it as a fresh image (with full resync) if it >> ever comes back. > > Why a full resync? With mdadm, it just keeps flagging the dirty chunks > so it only has to copy those when the other disk returns. Because it's really hard to guarantee anything when you experience a failure. The safe route is to discard any data on the failed drive. Certainly better than winding up with a subtly corrupt mirror. As I said before, if you experience that a lot, you should be using replication not mirroring. Yours, Petr.