Hi, first of all a great thank you to all developers and contributors. The Btrfs filesystem ist a great filesystem! Following common recommendations [1], I use these mount options on my main developing machine: noatime,autodefrag. This is desktop machine and it works well so far. Now, I'm also going to install several KVM virtual machines on this system. I want to use qcow2 files stored on SSD with a btrfs on it. In order to avoid bad performance with the VMs, I want to disable the Copy-On-Write mechanism on the storage directory of my VM images as for example described in [2]. My question now is: Is it safe to use the autodefrag mount option and to disable CoW for single directories which contain VM files at the same time? Is it even useful or may it harm? Thank you very much for insights and comments in advance. Best regards, jploz As requested in the wiki basic information about my fresh setup attached: uname -a Linux hostname 3.16.0-4-686-pae #1 SMP Debian 3.16.7-ckt7-1 (2015-03-01) i686 GNU/Linux btrfs --version Btrfs v3.17 btrfs fi show Label: none uuid: cc6492e7-a7a7-43f9-bba2-a1abe8635d36 Total devices 1 FS bytes used 4.00GiB devid 1 size 210.00GiB used 8.02GiB path /dev/sdb2 Label: 'DataHddBtr' uuid: aa3f41c0-5a60-4fd7-9365-8c99284e032c Total devices 1 FS bytes used 384.00KiB devid 1 size 480.00GiB used 2.04GiB path /dev/sda1 Btrfs v3.17 mount | grep btrfs /dev/sdb2 on / type btrfs (rw,noatime,ssd,space_cache,autodefrag) /dev/sda1 on /data/btr type btrfs (rw,noatime,space_cache,autodefrag) btrfs fi df / Data, single: total=7.01GiB, used=3.89GiB System, single: total=4.00MiB, used=16.00KiB Metadata, single: total=1.01GiB, used=114.39MiB GlobalReserve, single: total=48.00MiB, used=0.00B btrfs fi df /data/btr/ Data, single: total=8.00MiB, used=256.00KiB System, DUP: total=8.00MiB, used=16.00KiB System, single: total=4.00MiB, used=0.00B Metadata, DUP: total=1.00GiB, used=112.00KiB Metadata, single: total=8.00MiB, used=0.00B GlobalReserve, single: total=16.00MiB, used=0.00B dmesg | grep -i btrfs [ 2.693408] Btrfs loaded [ 2.756178] BTRFS: device fsid cc6492e7-a7a7-43f9-bba2-a1abe8635d36 devid 1 transid 393 /dev/sdb2 [ 2.756843] BTRFS: device label DataHddBtr devid 1 transid 9 /dev/sda1 [ 2.775447] BTRFS info (device sdb2): disk space caching is enabled [ 2.779944] BTRFS: detected SSD devices, enabling SSD mode [ 3.430997] BTRFS info (device sdb2): enabling auto defrag [ 3.431002] BTRFS info (device sdb2): disk space caching is enabled [ 3.548937] BTRFS info (device sda1): enabling auto defrag [ 3.548939] BTRFS info (device sda1): disk space caching is enabled [ 183.341398] BTRFS info (device sda1): enabling auto defrag [ 183.341403] BTRFS info (device sda1): disk space caching is enabled References: [1] https://btrfs.wiki.kernel.org/index.php/Gotchas [2] https://wiki.archlinux.org/index.php/Btrfs#Copy-On-Write_.28CoW.29 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
