What should be the characteristics of hard disk drive that is to be used for keeping the Airline reservation database.

What should be the characteristics of hard disk drive that is to be used for keeping the Airline reservation database. Assume that there is a centralized database that stores the information about all the flight reservations. Give reasons in support of your.

Answer: -
Hard disk drive is handled by the OS with limited user intervention. The disk storages considered the highest level of on-line memory. It holds the system programs such as the OS and compilers and some user programs and their data sets. It holds copies of present and past user programs and processed results and files. A typical centralized computer has the chache and main memory on a processor board and hard disks in an attached disk drive.

The Airline Reservation Database can occupy more space on the hard disk drive. Because database is centralizing, the capacity of the hard disk drive is too large. The hard disk drive consists of a motor to rotate the disk peak about its axis at a minimum speed of 3600 rps and maximum speed of 7200 rps. The hard disk drive has a set of magnetic heads mounted on arms.

Characteristics of hard disk drive : The characteristics of hard disk drive that is to be used for keeping the Airline reservation database (centralized) can be classified as following :

1) For fixed head, one read/write head per track is required. Heads can be mounted on a arm which extends to the centre of the disk. On the movable head disk one read/write head, which is fitted on an arm, is required. This arm allows head to position on any track of the platter.
2) The hard disks are normally mounted in a disk drive which consists of an arm and a shaft along with the electronic circuity for input-output of data. The disk rotates along with the shaft The hard disk is permanently mounted on the disk drive.
3) The magnetized coating is applied to both the sides of the platter in the hard disk drive. The data can be recorded on either side of this disk.
4) Hard disks have multiple platters stacked vertically at a distance of an inch. This is called disk pack. Disk pack contains cylinder which is the ring of all co-centric tracks. A disk pack can contain multiple heads mounted with the same arm.
5) The read/write heads are placed at a fixed distance from the platter, allowing an air gap. The gap of platter and head plays an important role. The smaller the size of the head the closer it should be to the platter surface in order to read and write properly. A smaller head allows greater data density on the disk.

6) Hard disk operate in semi-random mode of operation and normally are referenced block wise The data access time on hard disk has two components : Seek time (time to position the head on a specific track) and latency time (time required by a sector to reach below the read/write head).

Reasons:

1. The growth of processor speed has outstripped the growth in disk speed. This imbalance transforms traditionally CPU-bound applications to disk I/o bound applications. To obtain an improvement in application performance disk I/o bandwidth must be increased. The most common way to do this is by increasing the number of disk used to work on the problem.

2. Arrays of small diameter disks often have substantial cost power and performance advantages over large disk drives.

3. Disk array subsystems can be made highly reliable by storing a small amount of redundant information in the array without this redundancy, large disk arrays have unacceptably low data reliability because of their large number of components disks.

Redundant array of Inexpensive Disk (RAID) is used for a database server like Airline reservation database. RAID system balance load across a set of spindles providing a measure of automatic load balancing. When a single disk drive in a RAID array fails, the RAID system can recover the data without any need to resort to restoring a backup. These advantages come at some cost in terms of storage efficiency and performance, the deminent forms of RAID are RAID 5 and RAID 0.1.
For a database like Airline reservation databse, I would recommend minimum size of hard disk of 40 GB and the minimum size of cache of 512 KB.