Midterm 2: April 28th

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Midterm 2 April 28th

• Material
• Query processing and Optimization, Chapters 12
  and 13 (ignore 12.5.5, 12.7, 13.4.4 and 13.5)
• Transactions, Chapter 14
• Concurrency Control, Chapter 15, ignore 15.7 to
  15.10
• Recovery System, Chapter 16, ignore 16.8 and 16.9
• Google File System
• LRU-K, article by ONeils and Weikum
• Continuous Media, article by Ghandeharizadeh
  Muntz (1st 11 pages)
• COSAR-CQN

2
Enterprise Data Mangement

• Shahram Ghandeharizadeh
• Computer Science Department
• University of Southern California

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Challenge Managing Data is Expensive

• Cost of Managing Data is 100K/TB/Year
• Down time is estimated at thousands of dollars
  per minute.
• Loss of data results in lost productivity
• 20 Megabytes of accounting data requires 21 days
  and costs 19K to reproduce.
• 50 of companies that lose their data due to a
  disaster never re-open 90 go out of business in
  2 years!

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Centralize Management of Storage

• Before
• Data stored locally.

• After
• Data stored across the network at a central
  location.

Data
Network
Data
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Centralize Management of Storage

• Advantages
• Many clients share storage and data data
  remains available when a client fails.

Network
Data
6
Centralize Management of Storage

• Advantages
• Many clients share storage and data.
• Redundancy is implemented in one place protecting
  all clients from disk failure.

Network
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Centralize Management of Storage

• Advantages
• Many clients share storage and data.
• Redundancy is implemented in one place protecting
  all clients from disk failure.
• Centralized backup The administrator does not
  care/know how many clients are on the network
  sharing storage.

Network
8
Centralize Management of Storage

• Advantages
• Many clients share storage and data.
• Redundancy is implemented in one place protecting
  all clients from disk failure.
• Centralized backup The administrator does not
  care/know how many clients are on the network
  sharing storage.

Data Sharing
High Availability
Network
Data Backup
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Network failures

• What about network failures?
• Two host bus adapters per server,
• Each server connected to a different switch.

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Centralize Management of Storage

• Storage Area Network (SAN)
• Block level access,
• Write to storage is immediate,
• Specialized hardware including switches, host bus
  adapters, disk chassis, battery backed caches,
  etc.
• Expensive
• Supports transaction processing systems.

• Network Attached Storage (NAS)
• File level access,
• Write to storage might be delayed,
• Generic hardware,
• In-expensive,
• Not appropriate for transaction processing
  systems.

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Storage Area Network

• Centralize management of storage
• Storage Area Networks (SANs),
• Redundancy in data to tolerate disk failures,
• Regular backup,
• Disaster recovery.

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Concepts and Terminology

• Virtualization
• Available storage is represented as one HUGE disk
  drive, e.g., a SAN with a thousand 1.5 TB disk
  provides 1 Petabyte of storage,
• Available storage is partitioned into Logical
  Unit Numbers (LUNs),
• A LUN is presented to one or more servers,
• A LUN appears as a disk drive to a server.
• SAN places blocks across physical disks
  intelligently to balance load.

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Question

• Is it possible to present the same LUN to two
  different servers simultaneously?

16
Question

• Is it possible to present the same LUN to two
  different servers simultaneously? YES!
• Can two different servers read and write the
  files stored on the presented LUN?

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Question

• Is it possible to present the same LUN to two
  different servers simultaneously? YES!
• Can two different servers read and write the
  files stored on the presented LUN? Yes!
• What are the consequences?

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Concepts Backup

• Snapshot State of a LUN at one instance in
  time.
• Copy-on-write
• A snapshot consists of the original blocks of a
  LUN,
• Every time an application writes a block, SAN
  generates a new copy for the current LUN
  (snapshot maintains the original),
• Advantage copy of blocks in support of backup
  is generated on-demand.

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Copy-on-Write

• Original LUN and Snapshot taken midnight Sunday
  morning.

5
6
7
1
2
3
4
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Copy-on-Write

• Original LUN and Snapshot taken midnight Sunday
  morning.
• Write block 5 changes the current LUN to
• As blocks are written, the physical blocks of the
  snapshot materialize.

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7
Old 5
1
2
3
4
5
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Hot Standby

• An in-expensive server that is maintained on the
  side to assume responsibility for a failed
  server.
• Goal Minimize downtime.

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Summary

• SAN and NAS are shared-disk architecture,
• SAN is appropriate for transaction processing
  systems,
• Hardware alone is not a substitute for a
  parallel, high performance transaction processing
  system, e.g., Teradata, Oracle RAC, etc.