Physical Disk Structure

Disk Structure:

                          Disk drives are addressed as large 1-dimensional arrays of logical blocks, where the logical block is the smallest unit of transfer the 1-dimensional array of logical blocks is mapped into the sectors of the disk sequentially – Sector 0 is the first sector of the first track on the outermost cylinder – Mapping proceeds in order through that track, then the rest of the tracks in that cylinder, and then through the rest of the cylinders from outermost to innermost.

Physical Disk Structure

Cylinder 
The disc that makes up the hard disk is divided into tracks; tracks of all discs which have same track value are called a cylinder, so the cylinder is a pile of tracks with same track value of a hard disk. 

Head 
Normally, a disc has two heads for reading or writing data, one is for the top and the other one is for the opposite side; the head value means the disc location and side. 

Sector 
A track is composed of sectors and the number of sectors of all tracks on the hard disk is the same.Sector is the minimal storage unit of a hard disk; the size of one sector is always 512 bytes (rarely, it might be 1024, 2048 or 4096 bytes in some special hard disks). 

Components of Disk Drive

Components of Disk Drive are 

   

•         Platter and Read/Write Head
•         HAD
•         Power Connectors
•         Interface
•         Controller Board

Components of Disk Drive

Storage Options in Data Center

•      Magnetic Tape

4  Low cost solution for long term data storage

Ø  Preferred option for backup destination in the past

4  Limitations

Ø  Sequential data access

Ø  Single application access at a time

Ø  Physical wear and tear

Ø  Storage/retrieval overheads

•      Optical discs

4  Popularly used as distribution medium in small, single-user computing environments

4  Limited in capacity and speed

4  Write once and read many (WORM): CD-ROM, DVD-ROM

4  Other variations: CD-RW, Blu-ray discs

•      Disk drive

4  Most popular storage medium

4  Large storage capacity

4  Random read/write access

•      Flash drives

4  Uses semiconductor media

4  Provide high performance and low power consumption

Connectivity in DataCenter

Connectivity :

 

•      Interconnection between hosts or between a host and peripheral devices, such as storage 

•      Physical Components of Connectivity are:

4  Host interface card, port, and cable

•      Protocol = a defined format for communication between sending and receiving devices

4  Popular storage interface protocols: IDE/ATA and SCSI

Logical Volume Manager (LVM)

 Logical Volume Manager :

•      Responsible for creating and controlling host level logical storage

4  Physical view of storage is converted to a logical view

4  Logical data blocks are mapped to physical data blocks

•      One or more Physical Volumes form a Volume Group

4  LVM manages Volume Groups as a single entity

•      Logical volumes are created from the volume group

LVM Example: Partitioning and Concatenation

Application and application virtualization in DataCenter

Application :

•      A software program that provides logic for computing operations

•      Commonly deployed applications in a data center

4  Business applications – email, enterprise resource planning (ERP), decision support system (DSS)

4  Management applications – resource management, performance tuning, virtualization

4  Data protection applications – backup, replication

4  Security applications – authentication, antivirus

•      Key I/O characteristics of an application

4  Read intensive vs. write intensive

4  Sequential vs. random

4  I/O size

Application Virtualization :

Definition :

             It is the technique of presenting an application to an end user without any installation, integration, or dependencies on the underlying computing platform.

•      Allows application to be delivered in an isolated environment

4  Aggregates Operating System (OS) resources and the application into a virtualized container

4  Ensures integrity of Operating System (OS) and applications

4  Avoids conflicts between different applications or different versions of the same application