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What is SSD?

Solid State Disks are an exciting new technology using NAND FLASH RAM. We have seen this type of technology for a number of years in USB "Pen" drives. SSD using a more reliable, more expensive type of NAND FLASH to give reliability - essential to a Hard Disk Drive.

NAND FLASH RAM does have a limit to the number of times it can be written to. All SSD Manufacturers compensate for this using embedded software to wear level the writing operation to the disk. This ensures that no areas on the drive get written to more often than others, making the entire drive consistent in its wear-ability.

SSD is available in SATA, IDE and SCSI (Adtron only). It will not make a very slow, old PC miraculously quick. It will make new fast PC's even quicker.

What is the different between SSD and HDD

Traditional Hard disk technology involves an electric motor, rotating a platter of magnetic media, with a head sitting on an arm, microns away from this platter, reading the data through the head. The arm moving in and out to read all areas of this disk. The arm moves very fast and the rotation speed of the electric motor is stated on the drive (5400, 7200, 10000 rpm etc).

HDD drives are therefore restricted by these forces. Making the disk spin faster with increase heat, power and wear levels. Making the arm move faster will have the same constraints.

Solid State drives have no moving parts, therefore they have no "spin-up" or start up latency.
They can access all parts of the disk at an equal speed, so there are no fragmentation issues with SSD.
No moving parts, means no sound.
No moving parts, also means a lot less power consumption, so better for the environment and your laptop battery.
No moving parts, also means no risk of mechanical failure - so no head crash
No moving parts, also means that any shock applied to the drive or other environmental stresses (vibration, shaking) have no effect.


SSD is available in SATA, IDE and SCSI (Adtron only). It will not make a very slow, old PC miraculously quick. It will make new fast PC's even quicker.

Dispelling the Myths

Although NAND Flash has a theoretical maximum amount of writes that can be made to each cell. The manufacturers incorporate a wear-levelling algorithm to the circuitry/chip programming language so that it ensures that no particular area of NAND fash is written to more than any other. This is called wear-levelling and enables the manufacturer to give a warranty no matter what the application of the drive is used for.

MLC drives store multiple bits of data in each cell to store more data on smaller amounts of NAND Flash. Therefore each cell gets more action, than that of an SLC drive. SLC drives therefore have longer warranties than MLC drives. This enables you to choose your drive based on your requirement. For this reason SLC drives are usually chosen for Enterprise systems, MLC for consumer or desktop systems.

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Single Layer Cell

Single Layer Cell drives are quicker but are restricted to the capacity of the size of the RAM used. Each cell on the slab of silicon (there are millions of cells on each) has an on or off state. Voltage is measured within the cell to determine it's state. Let's say this voltage is measured between 0 and 100 ma. Anywhere above 1ma is read to be on. Below 1ma is off.

Multi Layer Cell

Multi Layer Cell drives can have larger data capacities but are slower than SLC drives. Here each cell can be split - so for a dual layer voltage between 1 and 50 and 51 and 100 doubles the capacity of the cell to store 2 lots of data. For a 4 layer cell between 1 and 25, 26 and 50, 51 and 75, 76 and 100 gives 4 layers of state within each cell. This of course takes longer to calculate which slows the drive down, but gives a greater data capacity. It also means a more complex controller card requiring greater accuracy.

Applications

The slow read/write speed of traditional spinning disks has caused developers to reverse engineer their applications to accomodate this negative effect. Enterprise database systems - hold common areas of the Database in RAM which is very fast, and then trickle the writes to disk "offline", behind the scenes.

With SSD this type of reverse engineering is no longer a bottleneck on the system and will allow for applications to have a more natural development structure. This will enable a huge change in the speeds of computer systems.


It is estimated that in the next few years all disk dives will be using Solid State technology.

Return on Investment

The true potential of SSD is starting to make waves in the enterprise and high end server application market. Having a much faster IO with faster access to data, enables systems to reach their potential and to do it cheaper. Traditionally, a large server room would be required with air conditioning, dual power (with redundancy/UPS systems) are required to host large clustered systems running a single application across many servers. Often this is to scale the application so that it comfortably accomodates hundreds or thousands of concurrent users.

SSD will enable these farms to reduce in size, hosting more users on smaller numbers of systems. Therefore giving a higher return on the investment of SSD.

SSD may seem an expensive option, but cutting the amount of hardware, environmentals and power to run the same application makes SSD a cheaper option.