1. Author Politehnica University of Bucharest Automatic Control and Computers Faculty Computer Science Department Scientific Advisor File System Freezing Solution Using Btrfs Vladimir-Andrei Olteanu vl.olteanu@gmail.com Drd. Ing. Octavian Purdil ă As. Drd. Ing. R ă zvan Deaconescu Bachelor Presentation Session - July 2010

2. Contents Goal Why Btrfs? Architecture Features Implementation Modified Btrfs module Logical subvolume cloning Logical subvolume deletion On-the-fly freezing / thawing Viewing the subvolume tree Future development 22.02.2016Bachelor Presentation Session - July 20102

3. Goal Freezing solution – Discarding changes to the FS RCS features 22.02.2016Bachelor Presentation Session - July 20103

4. Why Btrfs? Next default FS for most Linux distros? – Caveat: still unstable Subvolumes Snapshots COW COW-friendly B-trees 22.02.2016Bachelor Presentation Session - July 20104 CDEF AB XY B’ F’

5. Architecture frozen_butter Btrfs kernel space user space frozen_butter frozen_opsfrozen_tree 22.02.2016Bachelor Presentation Session - July 20105

6. Features Supported logical subvolume operations – Cloning, deleting, freezing, thawing – Optimizing for long-term use Tracking time of creation, freezing and thawing Tracking parent-child relationships 22.02.2016Bachelor Presentation Session - July 20106

7. Implementation Logical subvolume = 2 on-disk subvolumes – Base – Sandbox Manipulation when: – Mounting – Cloning / deleting / optimizing – Freezing / thawing 22.02.2016Bachelor Presentation Session - July 20107

8. Modified Btrfs module Superblock metadata Numbered subvolumes Mounting procedure IOCTLs Backwards compatible

9. Logical subvolume cloning 4 1 5 7 2 6 3 1 2 6 3 4 5 7 time 3467 25 1 22.02.2016Bachelor Presentation Session - July 20109 # frozen_butter /mnt /dev/sda1 –c

10. 346 7 5 1 Logical subvolume deletion 4 1 5 7 6 3 1 6 3 4 5 7 time 22.02.2016Bachelor Presentation Session - July 201010 # frozen_butter /mnt /dev/sda1 –d 2

11. On-the-fly freezing / thawing remount 22.02.2016Bachelor Presentation Session - July 201011 # mount /dev/sda1 /mnt# frozen_butter /mnt /dev/sda1 –f 1# umount /mnt # mount /dev/sda1 /mnt # frozen_butter /mnt /dev/sda1 –t 1

12. Viewing the subvolume tree # frozen_butter /mnt /dev/sda1 –p [1] INIT [2] name2 [3] name3 [4] name4 (frozen) [6] name6 [5] name5 [7] name7 Currently mounted: 3 After next mount: 2

13. Future development Kernel space – Offloading (almost) everything – Support for deleting nested subvolumes User space – Project-specific tools 22.02.2016Bachelor Presentation Session - July 201013

14. Thank you! Btrfs Subvolume Snapshot Freezing Thawing ? 22.02.2016Bachelor Presentation Session - July 201014