Disk Backup Through Algebraic Signatures For A Scalable Distributed Data Structure in SDDS-2002 System

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

Witold Litwin Witold.Litwin_at_dauphine.fr Riad
Mokadem Riad.Mokadem_at_dauphine.fr Thomas Schwartz
tjschwarz_at_scu.edu
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Plan
Introduction The SDDS-2002 Backup Scheme
Experimental performance analysis. Conclusion.
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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

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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

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The SDDS-2002 Backup Scheme File Backup
Client
Server Disks
? ?
? ?
? ?
? ?
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The SDDS-2002 Backup Scheme File Load
Load command Multicast)
Client



Server RAM Buckets
? ?
? ?
? ?
? ?
Server Disks
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Internal Organization of Bucket in SDDS
Data File
Index a few Kbytes up to MByte Data file
Dozens of Mbytes up to GBytes
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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
• Although 64 KB pages proved best for data page
  signature calculus speed
• 256 B for index

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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 pi antilog pi
• for each ? ?, ?2, ?3
• Sign ? ( P )? pi ? i i 1..n
• Sign ? (P) (Sign ?( P ), Sign ?2( P ),Sign ?m(
  P ))
• We put m 2 to SDDS-2002

i1,2...n
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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

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Experimental Performance SDDS-2002 Initial 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
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Initial File Store Time(Time Series)
Storage Time (Ms)
Number of record
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File Load 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
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File Storage Performance Analysis
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SHA-1 / Algebraic Signatures
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Algebraic / SHA-1 Signature Calculus Time
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Implementation in SDDS 2002Interactive Client
Interface
User interface
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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)
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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

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Thank You forYour Attention
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