Efficient P2P backup through buffering at the edge

S. Defrance, A.-M. Kermarrec (INRIA), E. Le Merrer, N. Le Scouarnec, G. Straub, A. van Kempen

Peer to Peer backup system

2 04/20/23

« Pure » P2P backup systems severely limited by:• Low availability • Asymmetric bandwidth (Low uplink speed)• Asynchrony

Exploit users’ ressources : each user provides storage space

Time To Backup (TTB) and Time to restore (TTR) data may be very high

Practical deployment is limited

Peer 2

0 h 12 h 24 h

Peer 1

CDN-assisted architecture

3 04/20/23

The performances of client-server systems are approached (in terms of Time To Backup and Time To Restore data)

However : • A centralized part remains• Not fully convenient for users

Server = Reliable component

Architecture proposed in P2P 2010 :

What we propose

4 04/20/23

Gateways are turned into stable buffering layers

To take into account the low-level structure of network (i.e the presence of gateways in home networks)

To use gateways to distribute the centralized part of the hybrid scheme

Home network

(LAN)

LAN

LAN

LAN

Mask the asynchrony between peers

Why gateways are good candidates ?

5 04/20/23

• Already present in users 'homes

• Storage capable (for buffering)

• Highly available

• At the frontier between a fast LAN and a slow WAN

Home network

Gateways are highly available

6 04/20/23

We periodically pinged a random set of static IP of a french ISP*

• 25,000 gateways

• For 7.5 months

*The trace is available at : http://www.thlab.net/~lemerrere/trace_gateways

10000

13000

16000

19000

22000

25000

Jul 1Sep 1

Nov 1

Jan 1Feb 11

Gate

ways

up

School holidays in France

•Average gateway availability : 86 %• Large part is very stable • A few have power-off habits (daily or holiday basis)

How does it work ?

7 04/20/23

Prepare (LAN

speed)

Backup (WAN speed)

Offload (LAN

speed)

How do we evaluate ?

8 04/20/23

Trace-based simulation using public traces • To model peers behavior :

-Skype 28 Days 1269 Peers AvailabilityMean = 0.5

-Jabber 28 Days 465 Peers AvailabilityMean = 0.27

Scenario:

Size of archive : 1GB Data creation : Poisson process(3 backups/month/user avg) Erasure code 50 simulations/curve

• To model gateways behavior : our gateway trace

• To model bandwidth uplink : trace from a study of residential broadband networks UplinkMean = 66 kB/s We randomly assign one gateway and one uplink speed to one peer of each trace

What do we evaluate ?

9 04/20/23

CDN-Assisted (CDNA)

Pure P2P(P2P)

Gateway-Assisted(GWA)

We compare :

We evaluate :

• Time To Backup (Hours)• Time To Restore (Hours)• Mean and Max data buffered (Mbytes)

TTB : Time between the backup request and the time when the last block has been completely uploaded

TTR : Time between the restore request and the time we downloaded enough data to reconstruct the file

• Time To Backup(Stored safely at remote place)

TTB & TTR (Skype trace)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

0.1 1 10 100

CD

F

Hours

CDNA & P2P

GWACDNA

P2P

90th Percentile of completed backup

GWA CDNA P2P

30 H 60 H 140 H

90th Percentile of completed restore

GWA CDNA P2P

3 H 40 H 40 H

• Time To Restore(Retrieve an archive locally)

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Scaling (Skype trace)

11 04/20/23

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8 9 10

TTR

(H

ours

)

Archive size (GB)

GWACDNA

P2P

Better scaling with archive size :

This enables users to backup larger amounts of data

• Low storage needs1GB archives: 2.5GB needed (99%)

Realistic for current gateways

Dimensioning (Skype trace)

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600 700

short

stack

Buff

er

Consu

med a

t each

peer\

\(Ave

rage in M

B)

Time (Hours)

Total

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

0 0.5 1 1.5 2 2.5 3 3.5 4

CD

F

Provisionned Buffer (Max in GB)

Total

Stopping backups

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Avera

ge s

tora

ge o

n g

ate

ways

(MB

)

• Average usage remains lowLess than 1MB hereData is really offloaded to peers Gateway effectively used as buffers

Conclusion

13 04/20/23

• Realistic architecture for P2P backup systems • Evaluation using trace-based simulation

• TTB and TTR are greatly reduced(Network connection can be used more efficiently)

• More convenient for users : Let to offload backup tasks quickly (LAN speed) from the user’s machine to the gateway

• Fully decentralized

• Trace of gateway availability

14 04/20/23

Thank you !