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Witold Litwin Witold.Litwin@dauphine.fr Riad Mokadem Riad.Mokadem @dauphine.fr - PowerPoint PPT Presentation


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Disk Backup Through Algebraic Signatures For A Scalable Distributed Data Structure in SDDS-2002 System. Witold Litwin Witold.Litwin@dauphine.fr Riad Mokadem Riad.Mokadem @dauphine.fr Thomas Schwartz tjschwarz@scu.edu. Plan. Introduction The SDDS-2002 Backup Scheme

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slide1
Disk Backup Through Algebraic Signatures ForA Scalable Distributed Data Structurein SDDS-2002 System

Witold Litwin Witold.Litwin@dauphine.fr

Riad Mokadem Riad.Mokadem@dauphine.fr

Thomas Schwartz tjschwarz@scu.edu

slide2
Plan

Introduction

The SDDS-2002 Backup Scheme

Experimental performance analysis.

Conclusion.

introduction
Introduction
  • Need for RAM SDDS storage to the disk
    • File Backup
      • Failure of a server
    • File Eviction
      • Sharing of RAM
        • Among different SDDS files
        • With other apps
introduction1
Introduction
  • Write to the disk only the parts (pages) changed since last backup
    • “Dirty bit” approach inapplicable
    • Page signature calculus: a possibility provided that:
        • Fast
        • Precise
        • Scalable
          • Shorter signatures may become longer without total recalculus
          • Not the case of SHA-1 nor of any other previous proposed schema
the sdds 2002 backup scheme file backup

Store command Multicast)

Server RAM Buckets

Distributed Storing

The SDDS-2002 Backup SchemeFile Backup

Client

Server Disks

the sdds 2002 backup scheme file load

Distributed Loding

The SDDS-2002 Backup SchemeFile Load

Load command Multicast)

Client

Server RAM Buckets

Server Disks

internal organization of bucket in sdds
Internal Organization of Bucket in SDDS

Data File

Index : a few Kbytes up to MByte

Data file : Dozens of Mbytes up to GBytes

page granularity
Page Granularity
  • Carefull choice
    • Smaller page
      • More individual writes if many random updates
      • Less data transferred if a few updades
    • Larger pages
      • Vice versa
    • Optimal size ?
      • Good question
    • Our choice
      • 16 KB for data
        • Although64 KB pages proved best for data page signature calculus speed
      • 256 B for index
page signature
Page Signature
  • Algebraic Signatures
  • Galois Field GF (216)
  • Log / Antilog multiplication
  • Page P has 2-byte symbols p1 , p2, ….pn
  • The signature formula is :
    • for each p’i = antilogp’i
    • for each  = : , 2, 3…
  • Sign ( P )= p’iii = 1..n
  • Sign (P)= (Sign ( P ), Sign 2( P ),…Sign m( P ))
  • We put m = 2 to SDDS-2002

i=1,2...n

experimental performance analysis hardware configuration
Experimental Performance AnalysisHardware Configuration
  • 1.8 GHz P4 Servers
  • 800 MHz P3 Client
  • 500 MHz P3 Name Server
  • 1 Gbs Ethernet
  • Windows 2000 Server OS
experimental performance sdds 2002 initial file store time no signature calculus
Experimental Performance SDDS-2002Initial File Store Time (No Signature Calculus)

Time

(Sec)

120

100

80

60

40

20

File Size: 393MO

25 000 Records

1 2 3 4

File servers

initial file store time time series
Initial File Store Time(Time Series)

Storage Time

(Ms)

Number of record

file load time
FileLoad Time

(Sec)

120

100

80

60

40

20

File Size :

393MO

1 2 3 4

# of servers

Practically the same as the 1st backup time

file storage performance analysis

Bucket size

(MB)

Number of record

Signature calculus (ms)

Signature Calculus per/MB

(ms)

Total

store time

(ms)

Store time for 0 % change

(ms)

Gain (%)

Store time for 5 % change

(ms)

Gain

(%)

1.88

100

46

24.46

562

50

91.1

65

88.43

2.7

150

78

28.8

781

82

89.51

95

87.83

17.6

1000

438

24.88

5078

438

91.38

453

91.07

158

10000

4068

25.74

46406

4071

91.23

4085

91.19

393

25000

11003

27.9

117859

11003

91.33

11018

90.65

File Storage Performance Analysis
sha 1 algebraic signatures

Bucket size

(Mb)

Number of record

Algebraic signature calculus (ms)

SHA-1

calculus

(ms)

Initial Store time with SHA-1

(ms)

Initial Store time with alg. sign.

(ms)

SHA-1 Store time for 5 % change

(ms)

Alg. sign Store time for 5 % change

(ms)

Gain

(%)

1.88

100

46

70

602

562

85

65

30

2.7

150

78

103

799

781

119

95

25

17.6

1000

438

680

5278

5078

697

453

53

158

10000

4068

6088

47906

46406

6102

4085

49

393

25000

11003

15403

119342

117859

15418

11018

40

SHA-1 / Algebraic Signatures
impl e mentation in sdds 2002 execution listing at the server
Implementation in SDDS 2002Execution Listing at the Server

1st Request for storage : New File Signature Calculus (375 ms) Disk write of all pages (4922 ms)

2nd Request for storage : No changes found (375 ms)

}

3rd Request for storage : 1 page changed (375 + 16 ms)

conclusion
Conclusion
  • The algebraic signature based file backup works
  • Present in SDDS-2002 prototype
  • Offers advantages over the traditional approach
    • No change to existing code
    • No run-time overhead
  • Future work
    • Signatures
      • Calculus, Alg. Properties, Apps…
    • Automatic SDDS File eviction