SSDs are developing quickly and the same goes for the standout models now on the market. In 2009, we had the Intel X25-M and OCZ Vertex / Crucial M225 SSDs based respectively on Intel and Indilinx controllers. In 2010, the arrival of various new players on the controller market shook things up: Marvell, who supplied the Crucial C300, and SandForce, whose controllers are used on the OCZ Vertex 2s and the Corsair Force Series.
Who will dominate in 2011?
This is what we’re going to try and find out in this report!
120 to 300 GB SSDs
At launch manufacturers usually send us the fairly high capacity versions first, though these aren’t necessarily the ones you’re likely to buy. The flagship models in the range, they generally give better levels of performance to the more reasonably priced versions that most of us will buy.
So then, Crucial sent us the 256 GB version of the M4, Intel who sent the Intel 320 300 GB and the Intel 510 250 GB and OCZ sent us the Vertex 3 240 GB . All well and good to compile an SSD report, but it’s obviously be better to be able to compare SSDs that are actually going to be bought! Thankfully, we were also able to get our hands on the Crucial M4 128 GB, the Intel 320 120 GB, the Intel 510 120 GB and the OCZ Vertex 3 120 GB, which we feel make our roundup a good deal more relevant.
With the exception of the Intel 510 SSDs, these new SSDs all use new 25nm flash memory produced by IMFT, the Intel / Micron subsidiary. The advantages of a finer engraving are clear, as you can see in this schema comparing two 34nm 4GB chips, one 25nm 8 GB chip and one 20nm 8 GB chip:
The finer the engraving, the less space the transistors take up and the smaller the final chip is! 4 GB at 34nm took up 172mm², 8 GB at 25nm takes up 167mm² and 8 GB at 20nm takes up 118mm². This also translates into lower production costs and, eventually, lower cost SSDs (lower cost per GB).
There is however a downside to the finer engraving, as it impacts negatively on the endurance of MLC flash cells. At 34nm, these cells are generally guaranteed for 5000 writes, against 3000 writes for a 25nm chip. On a 120 GB SSD with a controller that correctly distributes wear across the cells (wear leveling) and with write amplification of 1, you can in theory write 360 TB of data, or 197 GB a day! This is of course an ideal scenario and Intel is giving figures of 20 GB a day for five years and Crucial 20 GB a day for the M4s and 64 GB and 40 GB for its other SSDs. This isn’t really much of a problem as typical usage is somewhere between 5 and 10 GB.
There is one more point to note with respect to 25nm flash. The arrival of 8 GB chips has been combined with some structural modifications. The size of a page has gone up from 4 KB on a 34nm 4 GB chip to 8 KB, and the size of a block from 512 KB to 1 or even 2 MB. During reads or writes, the SSD works with pages and the load is therefore “only” doubled. Rewriting however takes place at block level and, to take a worst case scenario, rewriting 4 KB on a block that has already been used may mean reading it (2 MB), combining the old data with the new and then rewriting it (2 MB once again). There’s every incentive therefore for the controllers to get a headstart in freeing up unused pages, which is where TRIM comes in, so as to avoid this situation.