Author

Politehnica University of

Bucharest

Automatic Control and Computers

Faculty

Computer Science

Department

Scientific Advisor

File System Freezing Solution Using Btrfs

Vladimir-Andrei Olteanuvl.olteanu@gmail.com

Drd. Ing. Octavian PurdilăAs. Drd. Ing. Răzvan Deaconescu

Bachelor Presentation Session - July 2010

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

05.05.23 Bachelor Presentation Session - July 2010 2

Goal

• Freezing solution– Discarding changes to the FS

• RCS features

05.05.23 Bachelor Presentation Session - July 2010 3

Why Btrfs?

• Next default FS for most Linux distros?– Caveat: still unstable

• Subvolumes• Snapshots• COW• COW-friendly B-trees

05.05.23 Bachelor Presentation Session - July 2010 4

C D E F

A B

X Y

B’

F’

Architecture

frozen_butter

Btrfskernel space

user space

frozen_butter

frozen_ops frozen_tree

05.05.23 Bachelor Presentation Session - July 2010 5

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

05.05.23 Bachelor Presentation Session - July 2010 6

Implementation

• Logical subvolume = 2 on-disk subvolumes– Base– Sandbox

• Manipulation when:– Mounting– Cloning / deleting / optimizing– Freezing / thawing

05.05.23 Bachelor Presentation Session - July 2010 7

Modified Btrfs module

• Superblock metadata• Numbered subvolumes• Mounting procedure• IOCTLs• Backwards compatible

Logical subvolume cloning

4157

263

1

26

3

4

57

time

3 4 6 7

2 5

1

05.05.23 Bachelor Presentation Session - July 2010 9

# frozen_butter /mnt /dev/sda1 –c <id> <name>

3 4 6

7

5

1

Logical subvolume deletion

4157

63

1

63

4

57

time

05.05.23 Bachelor Presentation Session - July 2010 10

# frozen_butter /mnt /dev/sda1 –d 2

On-the-fly freezing / thawing

remount

05.05.23 Bachelor Presentation Session - July 2010 11

# mount /dev/sda1 /mnt# frozen_butter /mnt /dev/sda1 –f 1# umount /mnt

# mount /dev/sda1 /mnt

# frozen_butter /mnt /dev/sda1 –t 1

Viewing the subvolume tree

# frozen_butter /mnt /dev/sda1 –p[1] INIT [2] name2 [3] name3 [4] name4 (frozen) [6] name6 [5] name5 [7] name7Currently mounted: 3After next mount: 2

Future development

• Kernel space– Offloading (almost) everything– Support for deleting nested subvolumes

• User space– Project-specific tools

05.05.23 Bachelor Presentation Session - July 2010 13

Thank you!

• Btrfs• Subvolume• Snapshot• Freezing• Thawing

?05.05.23 Bachelor Presentation Session - July 2010 14