115. a. Disk array technology uses several disks in a single logical subsystem. To reduce or eliminate downtime from disk failure, database servers may employ disk shadowing or data mirroring. A disk shadowing, or RAID-1, subsystem includes two physical disks. User data is written to both disks at once. If one disk fails, all the data is immediately available from the other disk. Disk shadowing incurs some performance overhead (during write operations) and increases the cost of the disk subsystem because two disks are required. RAID levels 2 through 4 are more complicated than RAID-1. Each involves storage of data and error correction code information, rather than a shadow copy. Because the error correction data requires less space than the data, the subsystems have lower disk overhead.
116. Indicate the correct sequence of degaussing procedures for magnetic disk files.
1. Write zeros
2. Write a special character
3. Write ones
4. Write nines
a. 1, 3, and 2
b. 3, 1, 4, and 2
c. 2, 1, 4, and 3
d. 1, 2, 3, and 4
116. a. Disk files can be demagnetized by overwriting three times with zeros, ones, and a special character, in that order, so that sensitive information is completely deleted.
117. Which of the following is the best control to prevent a new user from accessing unauthorized file contents when a newly recorded file is shorter than those previously written to a computer tape?
a. Degaussing
b. Cleaning
c. Certifying
d. Overflowing
117. a. If the new file is shorter than the old file, the new user could have open access to the existing file. Degaussing is best used under these conditions and is considered a sound and safe practice. Tape cleaning functions are to clean and then to properly wind and create tension in the computer magnetic tape. Recorded tapes are normally not erased during the cleaning process. Tape certification is performed to detect, count, and locate tape errors and then, if possible, repair the underlying defects so that the tape can be placed back into active status. Overflowing has nothing to do with computer tape contents. Overflowing is a memory or file size issue where contents could be lost due to size limitations.
118. Which of the following data integrity problems can be caused by multiple sources?
a. Disk failure
b. File corruption
c. Power failure
d. Memory failure
118. b. Hardware malfunction, network failures, human error, logical errors, and other disasters are possible threats to ensuring data integrity. Files can be corrupted as a result of some physical (hardware) or network problems. Files can also become corrupted by some flaw in an application program’s logic. Users can contribute to this problem due to inexperience, accidents, or missed communications. Therefore, most data integrity problems are caused by file corruption.
Disk failure is a hardware malfunction caused by physical wear and tear. Power failure is a hardware malfunction that can be minimized by installing power conditioning equipment and battery backup systems. Memory failure is an example of hardware malfunction due to exposure to strong electromagnetic fields. File corruption has many problem sources to consider.
119. Which of the following provides network redundancy in a local-area-network (LAN) environment?
a. Mirroring
b. Shadowing
c. Dual backbones
d. Journaling
119. c. A backbone is the high traffic density connectivity portion of any communications network. Backbones are used to connect servers and other service providing machines on the network. The use of dual backbones means that if the primary network goes down, the secondary network will carry the traffic.
In packet switched networks, a backbone consists of switches and interswitch trunks. Switched networks can be managed with a network management console. Network component failures can be identified on the console and responded to quickly. Many switching devices are built modularly with hot swappable circuit boards. If a chip fails on a board in the device, it can be replaced relatively quickly just by removing the failed card and sliding in a new one. If switching devices have dual power supplies and battery backups, network uptime can be increased as well.
