The operating system generally treats removable disks as shared file systems, bu

Question

The operating system generally treats removable disks as shared file systems, but assigns a tape drive to only one application at a time. Give three reasons that could explain this difference in treatment of disks and tapes. Describe additional features that would be required of the operating system to support shared file-system access to a tape jukebox.
Would the applications sharing the tape jukebox need any special properties, or could
they use the files as though the files were disk-resident?

Explanation / Answer

a. Disks have fast random-access times, so they give good performance for interleaved access streams. By contrast, tapes have

high positioning times. Consequently, if two users attempt to

share a tape drive for reading, the drive will spend most of its

time switching tapes and positioning to the desired data, and

relatively little time performing data transfers. This performance

problem is similar to the thrashing of a virtual memory system

that has insuf?cient physical memory.

b. Tape cartridges are removable. The owner of the data may wish to

store the cartridge off-site (far away from the computer) to keep

a copy of the data safe from a ?re at the location of the computer.

c. Tape cartridges are often used to send large volumes of data

from a producer of data to the consumer. Such a tape cartridge is

reserved for that particular data transfer and cannot be used for

general-purpose shared storage space.

To support shared ?le-system access to a tape jukebox, the operating

system would need to perform the usual ?le-system duties, including

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