From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from walhalla.sjomar.eu ([141.105.125.198]:45851 "EHLO walhalla.sjomar.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751661AbbHGJyX (ORCPT ); Fri, 7 Aug 2015 05:54:23 -0400 Received: from hoefnix.localnet (a83-163-227-207.adsl.xs4all.nl [83.163.227.207]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: sjoerd@sjomar.eu) by walhalla.sjomar.eu (Postfix) with ESMTPSA id E7A13100279 for ; Fri, 7 Aug 2015 11:47:58 +0200 (CEST) From: Sjoerd To: linux-btrfs Subject: Re: btrfs raid1 metadata, single data Date: Fri, 07 Aug 2015 11:47:57 +0200 Message-ID: <1520215.AbHMhTRmNr@hoefnix> In-Reply-To: <201508071918.02231.russell@coker.com.au> References: <55C47136.2080402@render-wahnsinn.de> <201508071918.02231.russell@coker.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Friday 07 August 2015 19:18:02 Russell Coker wrote: > On Fri, 7 Aug 2015 06:49:58 PM Robert Krig wrote: > > What exactly is contained in btrfs metadata? > > Much the same as in metadata for every other filesystem. > > > I've read about some users setting up their btrfs volumes as > > data=single, but metadata=raid1 > > > > Is there any actual benefit to that? I mean, if you keep your data as > > single, but have multiple copies of metadata, does that still allow you > > to recover from data corruption? Or is metadata redundancy a benefit to > > ensure that your btrfs volume remains mountable/readable? > > If you have redundant metadata and experience corruption then you will know > the name of every file that has data corruption, this is really good for > restoring from backup. Also you will be protected against corruption of a > root directory causing massive data loss. > > If you have the bad luck to have certain metadata structures corrupted with > no redundancy then you can face massive data loss and possibly have the > entire filesystem become at least temporarily unusable. While corruption > of the root directory is unlikely it is possible. With "dup" metadata I've > seen a BTRFS filesystem remain usable after 12,000+ read errors. While we're at it: any idea why the default for SSD's is single for meta data as described on the wiki? (https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices#Filesystem_creation) I was looking for an answer why my SSD just had single metadata, while I expected it to be DUP and stumbled on this wiki article. Can't find a reason for why a SSD would be different? Cheers, Sjoerd