With more and more organizations relying on

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Unformatted text preview: f the file at the same time. 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 reliability tradeoffs: 1. 2. 3. 4. 5. 6. 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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