Title: Disk Backup Through Algebraic Signatures For A Scalable Distributed Data Structure in SDDS-2002 System
1Disk 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
2Plan
Introduction The SDDS-2002 Backup Scheme
Experimental performance analysis. Conclusion.
3Introduction
- 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
4Introduction
- 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
5The SDDS-2002 Backup Scheme File Backup
Client
Server Disks
? ?
? ?
? ?
? ?
6The SDDS-2002 Backup Scheme File Load
Load command Multicast)
Client
Server RAM Buckets
? ?
? ?
? ?
? ?
Server Disks
7Internal Organization of Bucket in SDDS
Data File
Index a few Kbytes up to MByte Data file
Dozens of Mbytes up to GBytes
8Page 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
9Page Signature
- 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
10Experimental Performance AnalysisHardware
Configuration
- 1.8 GHz P4 Servers
- 800 MHz P3 Client
- 500 MHz P3 Name Server
- 1 Gbs Ethernet
- Windows 2000 Server OS
11Experimental 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
12Initial File Store Time(Time Series)
Storage Time (Ms)
Number of record
13 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
14File Storage Performance Analysis
15SHA-1 / Algebraic Signatures
16Algebraic / SHA-1 Signature Calculus Time
17Implementation in SDDS 2002Interactive Client
Interface
User interface
18Implementation 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)
19 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
20Thank You forYour Attention
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