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Figure 8.26 shows a RAID unit having 10 disks. A large RAID unit can be composed of
more than one hundred disks and can have storage capacity of several terabytes (1
terabyte = 1012 bytes).
Note that the same RAID unit can be used in several different ways (combinations of
striping, mirroring, and error detection and correction) by changing the control software.
Depending on the various types of control software, there are the following commonly
accepted levels of RAID systems, each one with unique economic, performance and
7. RAID level 0: It uses striping.
RAID level 1: It uses mirroring.
RAID level 2: It uses striping plus error detection and correction.
RAID level 3: It uses striping with dedicated parity.
RAID level 4: It uses modified striping with dedicated parity.
RAID level 5: It uses modified striping with interleaved parity.
RAID level 0 + I: It uses striping and mirroring. With such a wide range of reliability features inbuilt in them, modern RAID systems
have mean time between data loss (MTBL) of well over a million hours, tlence they are
often considered as a basic unit for building reliable computer systems. With more and
more organizations relying on information technology to run their business, unscheduled interruptions have more serious consequences. As a result, today many organizations are
turning to the RAID as a safer way to store large amounts of data.
Automated Tape Library
An automated tape library is a set of magnetic tapes with a controller mounted in a single
unit. The unit has one or more tape drives to read and write data on the tapes in the tape
library. In case of units having multiple tape drives, it is possible to read/write data
from/to multiple magnetic tapes simultaneously resulting in faster data transfer rates.
Multiple drives also lead to improved reliability of the storage unit because if one of the
drives fails, the unit can continue to function with other drives at a slower speed. The unit
also has robotic arms to retrieve the appropriate tape from the tape library and mount it
on one of the...
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- Spring '14