Types of disk used in Storage

The disks in today’s storage environment are seeing a rapid change with the new type of disks available which produce more throughput & which are smaller in size that helps to put more disks into the disk array also the disk capacity are higher than its predecessor.

Let’s just dig in about this disks which are available in Storage platforms and understand what the technology that they are built on are, before that lets just touch upon those basic things that are important to consider when you think about disk.

A disk device has physical components and logical components. The physical components include disk platters and read/write heads. The logical components include disk slices, cylinders, tracks, and sectors.

All the hard disk drives are composed of same physical features, however quality of the parts inside the hard drive affects its performance, there are three important things that work together to give us the performance we want they are:

  1.      Disk Platter

The disk platter are made of aluminum or glass substrate it is then coated with magnetic surface which actually enables us to store the data in magnetic bits. The platters in a drive are separated by disk spacers and are clamped to a rotating spindle that turns all the platters in unison, there is a motor which is mounted right below the spindle which spins the platter at constant rate which is nothing but the RPM of the disk.

  2.       Drive Heads

The disk drive heads read and writes the data on these magnetic bits on the platter, there are usually two heads per platter which are sited on either side of the disk.

  3.       Actuator Arm

All the heads are attached to a single head actuator or actuator arm that moves the heads around the platters

As you can see that the hard disk are built by electro-mechanical components which has its performance limitation, which leads to the discovery of the disk that are built on flash based technology

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                                                                   SSD

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Solid state disk or SSD is the fastest of the disk available, it is basically built using the NAND-based memory as flash drive which don’t have any spinning parts of electromechanical disks which lead it to provide fast performance and low latency. Some new solid- state technology systems are designed for solid state as primary storage while using spinning disk as less expensive storage for less active data.

Enterprise flash drives are solid-state drives (SSD’s) that have been modified in order to meet the reliability required in an enterprise storage array and are widely used as the top tier in the automated storage tiering feature on the latest storage boxes

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                                                                     FC

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Fibre Channel is a hard disk drive interface technology designed primarily for high-speed, high volume data transfers in storage. Fibre Channel standards specify the physical characteristics of the cables, connectors, and signals that link devices.

Fibre Channel provides three topology options for connecting devices: point-to-point, arbitrated loop, and fabric (sometimes called “switched” or “switched fabric”).

With using Fibre Channel FC-AL loop we get a speed of 2, 4 to 6Gbps speed which are scalable (we can start with basic array and extend the loop as we needed), reliable (superior data encoding & error checking) which are built for mission critical environments

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                                                                      SAS

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SAS is the logical evolution of SCSI, including its long-established software advantage and its multi-channel, dual-port connection interface for enterprise storage which provides new levels of breakthrough speed and connectivity while retaining the functionality and reliability that is making SAS disks a good alternative for the FC disk in enterprise storage platform.

SAS disk are available in 10k and 15k RPM speed, the SCSI error-reporting and error-recovery commands on SAS are more functional than those on SATA drives

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                                                                       SATA

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SATA technology was developed directly to replace the legacy desktop parallel ATA (PATA) interface. The SATA interface is designed to meet the requirements of Entry to Enterprise-level storage deployments. SATA I provides a point-to-point data transfer of 1.5gbps but with the new SATA II disk we get a data transfer rate of 3 GBPS, this disk rotates at 5400, 7200 and 10k RPM

SATA disk offer better capacity then other disk types they may not give you high speed performance as SAS/FC/SSD disks but are of great use in environment where you have shared filesystem like NFS/CIFS/SMB or in low cost environments.

SATA drives use native command queuing, while SAS drives use tagged command queuing