2P13

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2P13

• Week 11

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RAID ControllersRedundant Array of Independent
(or Inexpensive) Disks
Level 0 -- Striped Disk Array without Fault
Tolerance Provides data striping (spreading out
blocks of each file across multiple disk drives)
but no redundancy. This improves performance but
does not deliver fault tolerance. If one drive
fails then all data in the array is lost. Level
1 -- Mirroring and Duplexing Provides disk
mirroring. Level 1 provides twice the read
transaction rate of single disks and the same
write transaction rate as single disks. Level 2
-- Error-Correcting Coding Not a typical
implementation and rarely used, Level 2 stripes
data at the bit level rather than the block
level.
A Guide to Managing and Maintaining your PC, 6e
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Level 4 -- Dedicated Parity Drive A commonly
used implementation of RAID, Level 4 provides
block-level striping (like Level 0) with a parity
disk. If a data disk fails, the parity data is
used to create a replacement disk. A disadvantage
to Level 4 is that the parity disk can create
write bottlenecks. Level 5 -- Block Interleaved
Distributed Parity Provides data striping at the
byte level and also stripe error correction
information. This results in excellent
performance and good fault tolerance. Level 5 is
one of the most popular implementations of RAID.
Level 6 -- Independent Data Disks with Double
Parity Provides block-level striping with parity
data distributed across all disks. Level 01 A
Mirror of Stripes Not one of the original RAID
levels, two RAID 0 stripes are created, and a
RAID 1 mirror is created over them. Used for both
replicating and sharing data among disks. Level
10 A Stripe of Mirrors Not one of the original
RAID levels, multiple RAID 1 mirrors are created,
and a RAID 0 stripe is created over these. Level
7 A trademark of Storage Computer Corporation
that adds caching to Levels 3 or 4. RAID S EMC
Corporation's proprietary striped parity RAID
system used in its Symmetrix storage systems.
A Guide to Managing and Maintaining your PC, 6e
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RAID 0 1 http//www.adtron.com/expertise/activer
aid.html
A Guide to Managing and Maintaining your PC, 6e
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RAID 5
RAID 5 ensures that if one of the disks in the
striped set fails, its contents can be extracted
using the information on the remaining
functioning disks.
A Guide to Managing and Maintaining your PC, 6e
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RAID 10
Striping Mirrors, improves performance and give
redundancy.
A Guide to Managing and Maintaining your PC, 6e
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Table 11.4 RAID Levels
N number of data disks m proportional to
log N
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Files

• Data collections created by users
• The File System is one of the most important
  parts of the OS to a user
• Desirable properties of files

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File Structure

• Provide a means to store data organized as files
  as well as a collection of functions that can be
  performed on files
• Maintain a set of attributes associated with the
  file
• Typical operations include
• Create
• Delete
• Open
• Close
• Read
• Write

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Structure Terms

• File

• Field

• basic element of data
• contains a single value
• fixed or variable length

• collection of similar records
• treated as a single entity
• may be referenced by name
• access control restrictions usually apply at the
  file level

Database
Record

• collection of related data
• relationships among elements of data are explicit
  
• designed for use by a number of different
  applications
• consists of one or more types of files

• collection of related fields that can be treated
  as a unit by some application program
• fixed or variable length

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File Management System Objectives

• Meet the data management needs of the user
• Guarantee that the data in the file are valid
• Optimize performance
• Provide I/O support for a variety of storage
  device types
• Minimize the potential for lost or destroyed data
• Provide a standardized set of I/O interface
  routines to user processes
• Provide I/O support for multiple users in the
  case of multiple-user systems

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The Pile

• Least complicated form of file organization
• Data are collected in the order they arrive
• Each record consists of one burst of data
• Purpose is simply to accumulate the mass of data
  and save it
• Record access is by exhaustive search

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The Sequential File

• Most common form of file structure
• A fixed format is used for records
• Key field uniquely identifies the record
• Typically used in batch applications
• Only organization that is easily stored on tape
  as well as disk

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Indexed Sequential File

• Adds an index to the file to support random
  access
• Adds an overflow file
• Greatly reduces the time required to access a
  single record
• Multiple levels of indexing can be used to
  provide greater efficiency in access

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Indexed File

• Records are accessed only through their indexes
• Variable-length records can be employed
• Exhaustive index contains one entry for every
  record in the main file
• Partial index contains entries to records where
  the field of interest exists
• Used mostly in applications where timeliness of
  information is critical
• Examples would be airline reservation systems and
  inventory control systems

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Direct or Hashed File

• Access directly any block of a known address
• Makes use of hashing on the key value
• Often used where
• very rapid access is required
• fixed-length records are used
• records are always accessed one at a time

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B-Trees

• A balanced tree structure with all branches of
  equal length
• Standard method of organizing indexes for
  databases
• Commonly used in OS file systems
• Provides for efficient searching, adding, and
  deleting of items

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B-Tree Characteristics
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B-Tree Characteristics

• every node has at most 2d 1 keys and 2d
  children or, equivalently, 2d pointers
• every node, except for the root, has at least d
  1 keys and d pointers, as a result, each internal
  node, except the root, is at least half full and
  has at least d children
• the root has at least 1 key and 2 children
• all leaves appear on the same level and contain
  no information. This is a logical construct to
  terminate the tree the actual implementation may
  differ.
• a nonleaf node with k pointers contains k 1 keys

• A B-tree is characterized by its minimum degree d
  and satisfies the following properties

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Inserting Nodes Into a B-Tree
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The End