Servers

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

FIGURE 14-10 Server with redundant NICs

RAID Level 0—Disk 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 0—disk stripping

RAID Level 1—Disk Mirroring

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

FIGURE 14-12 RAID Level 1—disk mirroring

RAID Level 3—Disk 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

RAID Level 3—Disk 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 3—disk stripping with parity ECC

RAID Level 5—Disk Stripping with Distributed Parity

• Data are written in small blocks across several disks

FIGURE 14-14 RAID Level 5—disk stripping with distributed parity

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

Data Backup

• Copy of data or program files created for archiving purposes

• Vault– Tape storage

library

FIGURE 14-15 Examples of backup tape media

Tape Backups

FIGURE 14-16 Tape drive on a medium or large network