Work:
A virtual tape library (VTL)has the same components as that of a physical tape library except that the majority of the components are presented as virtual resources. For backup software, there is no difference between a physical tape library and a virtual tape library.
Virtual tape libraries use disks as backup media. Emulation software has a database with a list of virtual tapes, and each virtual tape is assigned a portion of a LUN on the disk.
A virtual tape can span multiple LUNs if required. File system awareness is not required while using backup to disk because virtual tape solutions use raw devices.
Similar to a physical tape library, a robot mount is performed when a backup process starts in a virtual tape library. However, unlike a physical tape library, where this process involves some mechanical delays, in a virtual tape library it is almost instantaneous. Even the load to ready time is much less than in a physical tape library.
After the virtual tape is mounted and the tape drive is positioned, the virtual tape is ready to be used, and backup data can be written to it. Unlike a physical tape library, the virtual tape library is not constrained by the shoe shining effect. In most cases, data is written to the virtual tape immediately. When the operation is complete, the backup software issues a rewind command and then the tape can be unmounted. This rewind is also instantaneous. The virtual tape is then unmounted, and the virtual robotic arm is instructed to move it back to a virtual slot. Many times, even the buffering and speed adjustment features of a tape drive fail to prevent the gaps, causing the “shoe shining effect.” This results in the tape drive stopping and rewinding to the appropriate point. The tape drive resumes writing only when its buffer is full, adversely affecting backup performance. When the tape operation is complete, the tape rewinds to the starting position and it is unmounted. The robotic arm is then instructed to move the unmounted tape back to the slot. Rewind timecan range from several seconds to minutes.
Shoe shining effect is the repeated back and forth motion a tape drive makes when there is an interruption in the backup data stream.
Answer:
B.