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Tam Chantem, Philip Little and Faruck Morcos. iDIBS : Reliable and Efficient Distributed Backup. Improving Peer-to-Peer Backup Systems. Objective : Improve peer-to-peer backup techniques. Approach : Built on DIBS , an existing peer-to-peer backup system. Results : Improved 3 aspects of DIBS:

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Tam chantem philip little and faruck morcos

Tam Chantem, Philip Little and Faruck Morcos

iDIBS: Reliable and Efficient Distributed Backup


Improving peer to peer backup systems
Improving Peer-to-Peer Backup Systems

  • Objective: Improve peer-to-peer backup techniques.

  • Approach: Built on DIBS, an existing peer-to-peer backup system.

  • Results: Improved 3 aspects of DIBS:

    • Reliability, Network Load, and Computation Time.


Idibs

Erasure

Codes

iDIBS

Peer List

iDIBS

Peer

File

Encoding

Peer

Peer

Database


Idibs1

Erasure

Codes

iDIBS

Peer List

iDIBS

Peer

File

Encoding

Peer

Peer

Database


Backup and recovery

a

b

c

d

e

f

g

h

RS Encoder

a

d

g

j

i

j

b

e

h

k

k

l

c

f

i

l

Backup and Recovery

Encoding and Distributing:

Peer

File

Peer

Peer


Backup and recovery1

a

b

c

d

e

f

g

h

RS Decoder

a

d

j

i

j

b

k

k

l

c

i

l

Backup and Recovery

Recovering and Decoding:

Peer

File

Dead Peer

Peer


Peer list backups

?

Data

Peer

List

?

a

b

c

?

?

d

e

f

Peer-List Backups

Unmodified DIBS after a crash:

Do you have my data?

Client


Peer list backups1

?

Data

Peer

List

?

a

Peer

List

b

c

?

?

d

Peer

List

e

f

Peer-List Backups

iDIBS after a crash:

Do you have my peer list?

Client


Peer list backups2

Data

Peer

List

a

b

c

d

e

f

Peer-List Backups

iDIBS after a crash:

Client


Thresholds
Thresholds

  • K – Required number of pieces to recover

  • N – Total number of pieces transmitted

  • Redundancy level:

    • DIBS: N = 2K

    • iDIBS: Recovery when up to 1 peer is dead


Example
Example

Assume: Peers = 4 K = 5 N = 6

Peer 1

Peer 2

Peer 3

Peer 4

Can’t recover!!!

So, N = 8



Luby transform codes
Luby Transform Codes

  • Reed-Solomon (RS) codes not scalable

  • Luby Transform (LT) codes

    • Digital Fountain concept

    • Probabilistic nature

    • 15% redundancy needed for successful decoding

    • Flexible symbol size T, to speed up decoding


Implementation lt codes
Implementation: LT Codes

  • Encoder and Decoder modules

  • Encoder:

    • Calculates redundancy needed

    • Encodes and splits file depending on T, number of users, and probabilistic parameters

  • Decoder:

    • Decodes pieces

    • Reconstructs file


Idibs reliable and efficient distributed backup

Luby Transform Codes Encoder/Decoder Performance

LT codes vs. RS codes

Encoder T=256

Decoder T=256

Processing Time (sec)

File Size (Kb)


Idibs vs dibs network utilization behavior
iDIBS vs. DIBS network utilization behavior

  • DIBS network utilization is flat.

  • iDIBS has decreased network utilization. (OH when users<10)

  • Tradeoff in the theoretical minium is better in iDIBS.

  • Results shown for T=32, for larger numbers iDIBS plots are better!


The idibs tradeoff

iDIBS

Advantages

Disadvantages

LT codes are:

1. Faster than RS

2. Flexible performance

given T.

Decreased overall

Network Utilization.

Peer Lists:

1. Allow faster recovery.

2. Increase reliability.

LT codes are probabilistic.

As T > 256 decoding is less stable

LT need a minimum of 15% of extra overhead + ESI to decode.

Peer lists induce a small amount of overhead

The iDIBS tradeoff


Contribution
Contribution

We contributed to the improvement of DIBS in the following ways:

  • Increase of performancethrough the introduction of a new encoding technology. (LT codes)

  • Introduction of this encoding scheme to the application of peer-to-peer backup systems.

  • More Reliability through redesign of the system recovery scheme. (Peer-Lists)

  • Reduces Network utilization by changing the philosophy of number of transmitted pieces N and LT codes.



Implementation timeouts thresholds
Implementation: Timeouts & Thresholds

If: Peers > K then N = K + 1;else: PiecesPerPeer = 1;while PiecesPerPeer * (Peers - 1) < K do: PiecesPerPeer = PiecesPerPeer + 1; N = N * K;end if

If a peer is offline, recovery is still possible