DBMS

11. Define average latency time. 

The average latency time of the disk is one-half the time for a full rotation of the  disk. 

12. What is meant by data-transfer rate? 

The data-transfer rate is the rate at which data can be retrieved from or stored to  the disk. 

13. What is meant by mean time to failure? 

The mean time to failure is the amount of time that the system could run continuously without failure. 

14. What are a block and a block number? 

A block is a contiguous sequence of sectors from a single track of one platter.  Each request specifies the address on the disk to be referenced. That address is in the form of a block number. 

15. What are called journaling file systems? 

File systems that support log disks are called journaling file systems. 

16. What is the use of RAID? 

A variety of disk-organization techniques, collectively called redundant arrays of independent disks are used to improve the performance and reliability. 

17. Explain how reliability can be improved through redundancy? 

The simplest approach to introducing redundancy is to duplicate every disk. This technique is called mirroring or shadowing. A logical disk then consists of two physical disks, and write is carried out on both the disk. If one of the disks fails the data can be read from the other. Data will be lost if the second disk fails before the first fail ed disk is repaired. 

18. What is called mirroring? 

The simplest approach to introducing redundancy is to duplicate every disk. This technique is called mirroring or shadowing. 

19. What is called mean time to repair? 

The mean time to failure is the time it takes to replace a failed disk and to restore the data on it. 

20. What is called bit-level striping? 

Data striping consists of splitting the bits of each byte across multiple disks. This is called bit-level striping.