Asalamualikum

My Name Is Raza Umer.

BSCS Section 1A Roll No. 1027

Mass Storage Devices.Mass storage device are storage system

having storage capacity of several trillions of bytes of data.

They use multiple units of a storage media (such as multiple disks, multiple tapes, multiple CD-ROMs, etc.) as a single storage devices.

Types Of Mass Storage Devices.

Disk array using a set of megnetic disk. Automated tape library using a set of

megnetic tapes CD-ROM jukebox using a set of CD-ROMs.

Disk array.A disk array is a disk storage system which contains multiple disk drives.

A disk array is commonly known as a RAID (RedundantArray of Inexpensive disk) .

As a secondary storage device, provides enhanced Storage capacity, enhanced performance and enhanced reliability.Enhanced storage capacity is achieved by using multipledisks.Enhanced performance is achieved by using parallel data transfer technique from multiple disks.Enhanced reliability is achieved by using techniques such as mirroring or striping.

Mirroring and striping.

In mirroring, the system makes exact copies of files on two hard disksIn striping, a file is partitioned into smaller parts and different parts of the file are stored on diffetent disks.

A RAID Unit

Automated Tape Library.

a) Set of magnetic tapes and magnetic tape drives with a controller mounted in a single box, forming a single large storage unit.b) Large tape library can accommodate up to several hundred high capacity magnetic tapes bringing the storage capacity of the storage unit to several terabytes.c) Typically used for data archiving and as on-line data back up devices for automated back up in large computer centers.

CD-ROM Jukebox.

a) Set of CD-ROMs and CD-ROMs drives with a controller mounted in a single box, forming a single large storage unit.b) Large CD-Rom jukebox can accommodate up to several hundred CD-ROM disks bringing the storage capacity of the storage unit to several terabytes.c) Used for archiving read-only data in such applications as on-line museums, on-line digital libraries, on-line encyclopedia, etc

Storage Hierarchy.

Cache memory Main

memory

On-line, direct access andSequential-acces secondoryStorage devices such as hard diskOff-line direct access and sequential

Access secondary storage devices such asTape, floppy disk,zip disk etc.

Mass storage devices such as tape library, CD jukebox, etc.

Large capacitySlower access timeAnd lower cost per Bit stored

Smaller capacity, fasterAccess time, and higher Cost per bit stored