Midterm 2: April 28th Material:   Query processing and Optimization, Chapters 12 and 13 (ignore , 12.7, and 13.5)   Transactions, Chapter 14   Concurrency Control, Chapter 15, ignore 15.7 to   Recovery System, Chapter 16, ignore 16.8 and 16.9   Google File System   LRU-K, article by O’Neils and Weikum   Continuous Media, article by Ghandeharizadeh & Muntz (1 st 11 pages)   COSAR-CQN

Enterprise Data Mangement Shahram Ghandeharizadeh Computer Science Department University of Southern California

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!

Centralize Management of Storage Before   Data stored locally. After   Data stored across the network at a central location. Network Data

Centralize Management of Storage Advantages:   Many clients share storage and data: data remains available when a client fails. Network Data

Centralize Management of Storage Advantages:   Many clients share storage and data.   Redundancy is implemented in one place protecting all clients from disk failure. Network

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

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 High Availability Data Backup Data Sharing

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

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.

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

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.

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

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?

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?

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.

Copy-on-Write Original LUN and Snapshot taken midnight Sunday morning

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 Old 5 5

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

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.