1 Advanced Database Systems Dr. Fatemeh Ahmadi-Abkenari September 2013.
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Transcript of 1 Advanced Database Systems Dr. Fatemeh Ahmadi-Abkenari September 2013.
1
PHYSICAL DATA ORGANIZATION
RAID SYSTEMS
Advanced Database SystemsDr. Fatemeh Ahmadi-Abkenari
September 2013
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RAID Systems
Redundant Array of Independent/ Inexpensive Disks
A lower level approach to the performance bottleneck caused by
disk I/O
Characteristics:
Increasing the availability of data in crash time Better throughput than a single disk Concurrent handling of multiple request Improving the request involving large block of data Transfer time reduction
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RAID Systems
Terminology:
Mirroring Striping Chunks 3- The unit of data to be spread
2- Spread of data across an array of disks1- One type of redundant storage
RAID LEVELS:
BASIC LEVELS (0, 1, 3, 5) HYBRID LEVELS (01, 10, 03, 30, 50, 100, …)
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RAID Levels
Level 0
Level 0: Uses only Striping and no Redundancy A failure of a single disk is devastating
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RAID Levels
Level 1
Level 1: Uses no Striping and only Mirroring High durability Expensive for many applications
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RAID Levels
Level 3
Level 3: Uses Striping and a type of Redundancy Chunks are at byte level The (n+1)st disk is the Parity disk Parity disk stores the XOR of the corresponding
bytes on the other n disks High transfer rate Useful for application with real-time requirement
a b c = a XOR b
0 0 0
0 1 1
1 0 1
1 1 0
b c a
0 0 0
1 1 0
0 1 1
1 0 1
a b c d = a XOR b XOR c
0 0 0 0
0 0 1 1
0 1 0 1
0 1 1 0
1 0 0 1
1 0 1 0
1 1 0 0
1 1 1 1
RAID Levels Level 3
A1: 1 1 0 1 0 1 1 0A2: 0 1 1 1 1 0 0 0A3: 1 1 1 1 1 0 1 0
Ap (1-3): 0 1 0 1 0 1 0 0
RAID Levels Level 3
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RAID Systems Level 5
Level 5: Uses Striping and Redundancy Stores Parity information No single parity disk
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Hybrid RAID Systems
Level 10
Level 10:Combination of Level 0 and Level 1
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Hybrid RAID Systems
Level 01
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Hybrid RAID Systems
Level 30
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Hybrid RAID SystemsLevel 03
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Hybrid RAID Systems
Level 50
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Level 100
Hybrid RAID Systems
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Cylinder
Track
Spindle
Platter
Sector
Arm Assembly Read/Write Head
Disk Organization
Disk Organization
A: TrackB: Mathematical SectorC: Disk Sector (Data Unit)D: Cluster
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Disk Organization
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Disk OrganizationTerminology:
Page: The unit of data transferred with each I/O operation
Block: is a sequence of adjacent sectors on a track
Cache: An array of page-size buffers in main memory
Hit: If an application refer to an item in a page exists in cache
Trade-off
Choosing the number of sectors in a block (page size)
For Further Reading;
Database Systems, An application-Oriented Approach
Second EditionChapter 9
Michael Kifer, Arthur Bernstein, Philip M. LewisPearson, Addison Wesley Publication
2006