Data stored in RAM ( ) when the power of the computer is turned off.A.is held permanentlyB.permanently disappearsC.is held temporarilyD.temporarily disappears

正确答案：CE
C,E 解析：Explanation: Placing log files and the data files on different physical disks or independent volumes, and placing the log file of a drive that does not hold the operating system can improve database performance as it allows the frequently written to log file to exist a disk with its own read/write heads and thus less seek time.

Note: A Windows 2000 supports basic disks, in which physical disks are divided into partitions, and dynamic disks, in which disks are divided into volumes that can comprise an entire disk, two or more entire disks, portions of a disk, or portions of up to 32 physical disks.

A NTFS volume is volume that is formatted with the NTFS file system. Physical database design involves mapping the logical design onto physical media to allow for the data to be physically accessed and maintained as quickly as possible by taking advantage of the available hardware and software features. It is important to correctly design the database and to take advantage of hardware and software features early in the development cycle of a database application, because making changes to these components at a later stage it is difficult.

Incorrect Answers:
A: For redundancy and fault protection the log file can be placed on a mirrored volume. It would not be a good idea to put data files on a mirrored volume though. Performance when accessing the data would suffer.

Note: A mirrored volume is a fault-tolerant volume that duplicates data on two physical disks. It provides data redundancy as it copies the data on one volume to another volume on a different disk. When one of the physical disks fails, the data on the failed disk becomes unavailable, but the system can continue to operate by using the mirror disk. In such a set up, the data file and the log file will reside on the same drive. This will not improve database performance.

B: A mirrored volume cannot comprise of one volume only. It must comprise of two volumes on separate physical disks as a mirrored volume is a fault-tolerant volume that duplicates data on two physical disks. When one of the physical disks fails, the data on the failed disk becomes unavailable, but the system can continue to operate by using the mirror disk.

D: Data is written and read sequentially on extended volumes. As a result the data file and the log file will be placed on the same physical disk.

F: In this scenario the data file is separated into a primary data file, that uses the .mdf extension, and a secondary data file, that uses the .ndf extension. However, the secondary data file is placed on the same volume as the log file. This will lead to performance improvements only in cases where data is not read from the secondary data file.

G: Placing the data file and the log file on the same volume will not improve database performance as it will not allow parallel processing.

参考答案：A