Solid State Drives (SSD) Explained - Everything you need to know about making a decision in performance based storage

Article Number: 33 | Rating: 4.5/5 from 14 votes | Last Updated: Mon, Aug 22, 2011 at 10:31 AM

What is a SSD (Solid State Drive)?

SSD is the acronym for Solid State Drive. SSD's are highly reliable storage devices that use solid-state memory to store data. An SSD emulates a hard disk drive and is available in the typical interfaces IDE, SATA or SCSI.

Solid State Drives can withstand extreme shock, vibration, temperature, altitude and harsh environmental conditions while operating without compromising on data integrity. Since there are no moving parts involved, data access time occurs as quickly as 0.1ms compared to typical consumer hard drives with spinning disks that can take 10-15ms, on average.

Standard models operate in temperatures of 0 - 70° C. and special industrial models can withstand operating temperatures of -40 - 85° C. SSD's are the same size and shape as traditional desktop hard drives (available in 1.8-inch, 2.5-inch, and 3.5-inch form factors) and utilize the same connectors making them easy to install in traditional PC based equipment.

What is the difference between SLC and MLC Solid State Drives?

There are two types of NAND Flash chips available in Solid State Drives. Single-level cell (SLC) and multi-level cell (MLC). Both are similar in design and even look the same but their differences are quite significant.

What is SLC?
Single Level Cell (SLC) flash outperforms Multi Level Cell (MLC) flash.

What is MLC?
Multi Level Cell (MLC) flash has low cost benefits, but performs at slower speeds.

Advantages of SLC over MLC

SLC flash accesses and writes to the NAND flash chips much faster, by using "simpler" control logic with 1 bit versus the 2 bits used by MLC flash.
The program operations in SLC chips last 100,000 cycles, ten times longer than MLC.
At a first glance the SLC drives appear to be much more expensive than MLC. However, when you consider the increased performance, higher reliability and increased lifespan the aggregate cost is much lower for the SLC based units.

Advantages/Disadvantages of SLC and MLC based Solid State Drives

Features	SLC	MLC
High Density	Lower Capacities	Higher Capacities
Low Cost per Bit	Higher than MLC	Lower Cost
Operating Temperature Range	(industrial, more rugged)	(commercial, less rugged)
Low Power Consumption	Low Power Better Performance	Not as efficient as SLC
Write/Erase Speeds	Best Performance	Not as good as SLC
Write/Erase Endurance	Best Performance	Not as good as SLC
Density	16Mbit	32Mbit/64Mbit
Block Size	64Kbyte	128Kbyte
Architecture	x8	x8 / x16

The above performance factors make SLC based Solid State Drives an excellent fit for mission critical and important applications where reliability, performance and long term support are desired. MLC based Solid State Drives are ideal for applications that are not as critical and where saving costs is a tradeoff for a bit less performance and long term reliability.