Storage and Storage Devices

By

Nilabh Verma

Storage Measurement Bit (b)

Nibble (n)

Byte (B)

Kilo Byte (KB)

Mega Byte (MB)

Giga Byte (GB)

Tera Byte (TB)

Peta Byte (PB)

Exa Byte (EB)

Zetta Byte (ZB)

Yotta Byte (YB)

Storage Characteristics

Can be Internal, External & Remote

Are nonvolatile

Two main things for storage:

– Device

– Media Mainly of four types:

– Magnetic Disks

– Optical Disks

– Tape

– Mobile Storage

Magnetic Disk

Most commonly used in today's storage systems.

Use mangnetic particles to store data on disk surface.

Data held on a disc in block fomed by tracks and sectors.

Tracks and sectors are created when disk is first formatted.

Data written and read by read/write heads.

Common types:

– Hard disks

– Floppy disks

– Zip disks Important to keep away from magnetic field.

Floppy Disk & Drive

Low capacity removable disk.

Mostly of 3.5” and holds 1.44/2.8 MB.

Not widely used today.

Sometimes reffered as a legacy drive.

Generally use PATA interface. Also available in USB.

Zip drive works similar with 100 to 250 MB of storage.

Hard Disk Drive High capacity disk.

Most common media of storage.

Use one or more metal magnetic disks.

Can be internal, external or remote.

Typically holds 80 GB to several Tbs.

Generally use following interface:

– PATA

– SATA

– SCSI

– USB

Hard Disk Drive High capacity disk.

Most common media of storage.

Use one or more metal magnetic disks.

Can be internal, external or remote.

Typically holds 80 GB to several Tbs.

Generally use following interface:

– PATA

– SATA

– SCSI

– USB

Optical Disk Drive High capacity disk which store data optically.

Can be internal or external.

Can be read only, recordable or rewritable.

Standard sized disk is 120 mm. Minis are 80 mm.

Standard CD holds upto 700 MB of data.

Standard DVD holds 4.7 GB (single layer) or 8.5 GB (double layer) of data.

High definition DVD or blue-ray disks can hold upto 50 GB typically (17-27 GB) of data.

Generally use following interface:

– PATA

– SATA

– USB

Optical Disk Drive Read only disks can be

– Read but no write.

– CD/DVD of same storage capacity. Recordable disks can be

– Written to but can't be erased or resuse.

– CD/DVD of same storage capacity. Rewritable disks can be

– Written, erased and overwritten just like a magnetic disk. Needs software to write (not necessary).

– CD/DVD of same capacity. All disks use the appropriate device to perform task.

DVD writer can handle almost kind of tasks.

Optical Disk Drive Read only disks can be

– Read but no write.

– CD/DVD of same storage capacity. Recordable disks can be

– Written to but can't be erased or resuse.

– CD/DVD of same storage capacity. Rewritable disks can be

– Written, erased and overwritten just like a magnetic disk. Needs software to write (not necessary).

– CD/DVD of same capacity. All disks use the appropriate device to perform task.

DVD writer can handle almost kind of tasks.

Flash Memory Systems No moving parts, less vibration, less power, makes

no sound, ultra portable, easy to use.

Can be in form of USB or card flash disks.

Can be directly connected with system or through appropriate card reader.

Flash cards can be of 1 GB to 8 GB or higher. Commonly used in mobiles, gaming systems.

USB flash drive can be of 2 GB to 64 GB or higher. Commonly used as a magnetic disks.

Storage for Large Computers

Usually use a storage server.

Containing multiple high spped HDDs.

Generally used in big corporates having

– Multiple servers.

– Hundreds of users.

– Tremendous amount of data.

DAS, NAS and SAN Direct Attached Storage (DAS)

– Most basic type of storage.

– Simple storage which is directly connect to the server.

Network Attached Storage (NAS)

– Storage server connect to a network to provide storage for computer on that network.

– Use TCP/IP protocol, Low performance. Storage Area Network (SAN)

– Network of storage devices that provides storage for another network of computers.

– Use fiber channel.

– Generally use RAID, Backup and restore, High performance, less load on network.

RAID Redundant Arrays of Indipendent Discs (RAID)

is a method of storing data on two or more hard drives that work together to do the job of larger drive.

– Usually involves recording redundant copies of stored data.

– Most commonly used

• RAID 0: Stripping (atleast 2 disks, usage n).

• RAID 1: Mirroring (atleast 2 disks, usage n/2).

• RAID 5: Stripping with distributed parity (atleast 3 disks, usage n-1).

Magnetic Tape Systems Works similar as magnetic disk.

Primarily used for backup.

Low cost per MB.

Mostly in form of cartridge tape.

Can be individual or with tape library.

Capacity from 4 GB to several TBs.