From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from postfix.iai.uni-bonn.de ([131.220.8.4]:50073 "EHLO postfix.iai.uni-bonn.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752579AbaGPWRS (ORCPT ); Wed, 16 Jul 2014 18:17:18 -0400 Received: from [192.168.0.57] (p5B0A04FC.dip0.t-ipconnect.de [91.10.4.252]) by postfix.iai.uni-bonn.de (Postfix) with ESMTP id 422805C442 for ; Thu, 17 Jul 2014 00:17:15 +0200 (MEST) (envelope-from ochmann@informatik.uni-bonn.de) (envelope-to linux-btrfs@vger.kernel.org) (1) (internal use: ta=1, tu=1, te=1, am=P, au=ochmann) Message-ID: <53C6FA3D.9010803@informatik.uni-bonn.de> Date: Thu, 17 Jul 2014 00:18:37 +0200 From: Sebastian Ochmann MIME-Version: 1.0 To: linux-btrfs@vger.kernel.org Subject: Is it safe to mount subvolumes of already-mounted volumes (even with different options)? Content-Type: text/plain; charset=ISO-8859-1; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: Hello, I'm sharing a btrfs-formatted drive between multiple computers and each of the machines has a separate home directory on that drive. The root of the drive is mounted at /mnt/tray and the home directory for machine {hostname} is under /mnt/tray/Homes/{hostname}. Up until now, I have mounted /mnt/tray like a normal volume and then did an additional bind-mount of /mnt/tray/Homes/{hostname} to /home. Now I have a new drive and wanted to do things a bit more advanced by creating subvolumes for each of the machines' home directories so that I can also do independent snapshotting. I guess I could use the bind-mount method like before but my question is if it is considered safe to do an additional, "regular" mount of one of the subvolumes to /home instead, like mount /dev/sdxN /mnt/tray mount -o subvol=/Homes/{hostname} /dev/sdxN /home When I experimented with such additional mounts of subvolumes of already-mounted volumes, I noticed that the mount options of the additional subvolume mount might differ from the "original" mount. For instance, the root volume might be mounted with "noatime" while the subvolume mount may have "relatime". So my questions are: Is mounting a subvolume of an already mounted volume considered safe and are there any combinations of possibly conflicting mount options one should be aware of (compression, autodefrag, cache clearing)? Is it advisable to use the same mount options for all mounts pointing to the same physical device? Best regards, Sebastian