Servers

1
Servers

• Redundant Array of Inexpensive Disks (RAID)
• A group of hard disks is called a disk array

FIGURE 14-10 Server with redundant NICs
2
RAID Level 0Disk Stripping

• Simple implementation of RAID in which data are
  written in 64 KB blocks equally across all disks
  in the array

FIGURE 14-11 RAID Level 0disk stripping
3
RAID Level 1Disk Mirroring

• Data from one disk are copied to another disk
  automatically as the information is written

FIGURE 14-12 RAID Level 1disk mirroring
4
RAID Level 3Disk Stripping with Parity ECC

• Disk stripping with a special type of error
  correction code (ECC)
• Term parity refers to the mechanism used to
  verify the integrity of data by making the number
  of bits in a byte sum to either an odd or even
  number

TABLE 14-1 Use of parity bits to achieve parity
5
RAID Level 3Disk Stripping with Parity ECC

• Parity error checking
• Process of comparing the parity of data read from
  disk with the type of parity used by the system

FIGURE 14-13 RAID Level 3disk stripping with
parity ECC
6
RAID Level 5Disk Stripping with Distributed
Parity

• Data are written in small blocks across several
  disks

FIGURE 14-14 RAID Level 5disk stripping with
distributed parity
7
Server Mirroring andServer Clustering

• Server mirroring
• Fault tolerance technique in which one server
  duplicates the transactions and data storage of
  another
• Server clustering
• Fault tolerance technique that links multiple
  servers together to act as a single server

8
Data Backup

• Copy of data or program files created for
  archiving purposes
• Vault
• Tape storage library

FIGURE 14-15 Examples of backup tape media
9
Tape Backups
FIGURE 14-16 Tape drive on a medium or large
network