author politehnica university of bucharest automatic control and computers faculty computer science...

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