PROCESSOR TYPES (CONT’D)
Every consumer SSD company has adapted SandForce processors into their SSD family except Samsung and Intel although there is evidence that Samsung will soon release a 520 Series SSD for enthusiasts which contains the SandForce SF-2281 processor.
The other family of processors are those that do not use compression and are common in processors manufactured by Marvell, Intel, Samsung, and some lesser known names such as JMicron and Phison. The below picture is of a Crucial M4 512GB SATA 3 SSD which utilizes the Marvell 9174 controller.
NAND FLASH MEMORY
The sole purpose of NAND flash memory is to provide storage for your data somewhat similar to that of the magnetic disk of a hard drive. In the Crucial 512GB we see above, there are 16 memory modules of 32GB capacity each for a total of 512GB. Typically, all SSDs are normally advertised in capacities that directly reflect the memory module itself which traditionally is a power of 4. A single module could have been as low as 4GB where now they can reach 64GB. This is why we would normally see 32, 64, 128, 256, 512GB SSDs advertised although manufacturers such as Intel have ventured off the beaten path to advertise capacities of 320GB as we saw in our review of the Intel 320 Series 300GB SATA 2 SSD.
Performance of non-compressed SSDs can also be affected by the number of die within the memory which is the reason that we see different performance specifications for different capacity drives. This was initially very visible in the Intel X25m 160GB SSD which was an excellent SSD although its maximum write speeds was limited to just over 100MB/s transfer speed.
“SandForce Driven” SSDs can easily be spotted as their drive capacity goes against the grain. Whereas we spoke of capacities of 32, 64, 128, 256 and 512GB above, companies that utilize SandForce SSDs have their product advertised in capacities that are typically 30, 60, 120, 240, and 480GB. This is because SandForce is able to improve the performance and lifespan of their product through their firmware and over provisioning, over provisioning which typically steals away 7% of NAND flash memory for the consumer and as high as 28% for enterprise.
OVER PROVISIONING AND DRAM CACHE MEMORY
When SSDs were first introduced to the consumer, capacity was a very limiting factor and people soon realized that SSD performance slows significantly when it approaches being full. Fortunately, there had been a great deal of advance which has relieved this performance decline, for the most part and it comes by way of a DRAM cache for non-compressed drives. We see cache modules in use by Intel, Samsung, Crucial and others that use Marvell, JMicron and Phison controllers.
SandForce does not use a cache as it takes control of that 7/28% over provisioning for just that purpose and it’s end result is sustained performance and a longer lifespan overall.
To show how really advanced SSDs and their technology has become, a ‘SandForce Driven’ SSD is able to monitor itself and if a cell/page/block of memory were to fail, the firmware actually recognizes this and swaps the information to a portion of the over provisioning where it is then remapped. Unlike a hard drive which will lose some capacity and scream corrupted cells, the SSD user would never have knowledge of the repair and the SSD would not suffer any loss of capacity.