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Unformatted text preview: ckup storage medium for data
stored on on-line devices such as a disk. During backup or recovery process, backup
tapes are normally processed continuously from beginning to end because there is seldom
a need for selective access of records. Hence there is no need to start and stop the backup
tape after every few records. Based on these observations, researchers came out with a
special type of quarter-inch streamer tapes that eliminate the need for the start/stop
operation of traditional tape drives for half-inch tape reels or tape cartridges. These tapes
are J4 inch wide and are sealed in a cartridge. Their tape drives are very similar in look
and mechanical operation to the tape drives of half-inch tape cartridges.
Unlike the half-inch tapes, which use parallel representation for data recording, these
tapes use serial representation for data recording. That is, the data bits are aligned in a
row, one after another in tracks. A streamer tape can have from 4 to 30 tracks, depending
on the tape drive. Depending on the tape drive, the read/write head reads or writes data on
one, two, or four tracks at a time. Figure 8.10 shows a streamer tape having 8 tracks on
which data are recorded two tracks at a time. That is, data are first written on the top two
tacks for the entire length of the tape or until the data are exhausted. If the end of the tape
is reached while data recording, the tape is rewound, the read/write head is positioned on
the next two tracks, and data recording continues in a similar manner.
As there is no start/stop mechanism, streamer tape drives can read/write data more
efficiently than the traditional tape drives that stop and restart the tape movement at each
IBG. Moreover, streamer tape drives also make more efficient utilization of tape storage
area. Typically, streamer tapes use 97% of the tape for data storage, whereas traditional
start/stop tapes use only 35% to 70%, depending on the blocking factor. Typical
capacities of streamer tape drives used in personal computers varies from 50 MB to 500
Streamer tapes are...
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This document was uploaded on 04/07/2014.
- Spring '14