Table 6.1 Physical Characteristics of Disk Systems Head Motion Fixed head (one per track) Movable head (one per surface) Disk Portability Nonremovable disk Removable disk Sides Single sided Double sided Platters Single platter Multiple platter Head Mechanism Contact (floppy) Fixed gap Aerodynamic gap (Winchester)Table 6.4 RAID Comparison (page 1 of 2) Level Advantages Disadvantages Applications 0 I/O performance is greatly improved by spreading the I/O load across many channels and drives No parity calculation overhead is involved Very simple design Easy to implement The failure of just one drive will result in all data in an array being lost Video production and Editing Image editing Pre-press applications Any application requiring high bandwidth 1 100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk Under certain circumstances, RAID 1 can sustain multiple simultaneous drive failures Simplest RAID storage subsystem design Highest disk overhead of all RAID types (100%) - inefficient Accounting Payroll Financial Any application requiring very high availability 2 Extremely high data transfer rates possible The higher the data transfer rate required, the better the ratio of data disks to ECC disks Relatively simple controller design compared to RAID levels 3,4 & 5 Very high ratio of ECC disks to data disks with smaller word sizes - inefficient Entry level cost very high - requires very high transfer rate requirement to justify No commercial implementations exist / not commercially viableTable 6.4 RAID Comparison (page 2 of 2) 3 Very high read data transfer rate Very high write data transfer rate Disk failure has an insignificant impact on throughput Low ratio of ECC (parity) disks to data disks means high efficiency Transaction rate equal to that of a single disk drive at best (if spindles are synchronized) Controller design is fairly complex Video production and live streaming Image editing Video editing Prepress applications Any application requiring high throughput 4 Very high Read data transaction rate Low ratio of ECC (parity) disks to data disks means high efficiency Quite complex controller design Worst write transaction rate and Write aggregate transfer rate Difficult and inefficient data rebuild in the event of disk failure No commercial implementations exist / not commercially viable 5 Highest Read data transaction rate Low ratio of ECC (parity) disks to data disks means high efficiency Good aggregate transfer rate Most complex controller design Difficult to rebuild in the event of a disk failure (as compared to RAID level 1) File and application servers Database servers Web, e-mail, and news servers Intranet servers Most versatile RAID level 6 Provides for an extremely high data fault tolerance and can sustain multiple simultaneous drive failures More complex controller design Controller overhead to compute parity addresses is extremely high Perfect solution for mission critical applicationsTable 6.5 Optical Disk Products CD Compact Disk. A nonerasable disk that stores digitized audio information. The standard system uses 12-cm disks and can record more than 60 minutes of uninterrupted playing time. CD-ROM Compact Disk Read-Only Memory. A nonerasable disk used for storing computer data. The standard system uses 12-cm disks and can hold more than 650 Mbytes. CD-R CD Recordable. Similar to a CD-ROM. The user can write to the disk only once. CD-RW CD Rewritable. Similar to a CD-ROM. The user can erase and rewrite to the disk multiple times. DVD Digital Versatile Disk. A technology for producing digitized, compressed representation of video information, as well as large volumes of other digital data. Both 8 and 12 cm diameters are used, with a double-sided capacity of up to 17 Gbytes. The basic DVD is read-only (DVD-ROM). DVD-R DVD Recordable. Similar to a DVD-ROM. The user can write to the disk only once. Only one-sided disks can be used. DVD-RW DVD Rewritable. Similar to a DVD-ROM. The user can erase and rewrite to the disk multiple times. Only one-sided disks can be used. Blu-Ray DVD High definition video disk. Provides considerably greater data storage density than DVD, using a 405-nm (blue-violet) laser. A single layer on a single side can store 25 Gbytes.Table 6.6 LTO Tape Drives LTO-1 LTO-2 LTO-3 LTO-4 LTO-5 LTO-6 Release date 2000 2003 2005 2007 TBA TBA Compressed capacity 200 GB 400 GB 800 GB 1600 GB 3.2 TB 6.4 TB Compressed transfer rate (MB/s) 40 80 160 240 360 540 Linear density (bits/mm) 4880 7398 9638 13300 Tape tracks 384 512 704 896 Tape length 609 m 609 m 680 m 820 m Tape width (cm) 1.27 1.27 1.27 1.27 Write elements 8 8 16
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