For SSD enthusiasts, SandForce is an easily recognized name. Both generations of SandForce controllers launched with impressive performance for their time, partly thanks to a novel approach in controller design that remains unique to SandForce today. The announcement we’re talking about here will make for the first controller to benefit directly from LSI’s expertise since it acquired SandForce.
It is with this context in mind that the third generation SF-3700 controller family has been completely redesigned from the ground up. Previous technologies such as DuraWrite and RAISE have been kept in the new, modular 40nm controller design, but things begin to differ from there. The clearest example is that the SF-3700 family has the capability to utilize both SATA 6Gb/s and PCI Express 2.0 x4 interfaces without the need for an intermediary chip. The controller is also capable of addressing Toggle, ONFI, and even TLC types of NAND, as well.
With the exception of Intel’s first in-house controller which utilized 10-channels, SSD controllers typically rely on 8-channel designs with the occasional 4-channel variant for the budget market. LSI decided to take the middle ground between Intel and the norm by designing the SF-3700 with 9-channels. This is where RAISE (Redundant Array of Independent Silicon Elements) comes into play. In previous SandForce designs, RAISE would protect against a single page or block failure in a similar fashion to how RAID works, but just like RAID some capacity must be sacrificed for the parity information. But now RAISE has the potential to offer up to a full NAND die of redundancy if OEMs wish. This optional level of redundancy would have an even larger reduction in drive capacity (seen by the end user) as the trade-off, however the addition of an optional ninth die (hence the nine channels) would provide sufficient space for this purpose without the need to heavily over-provision the drive.
DuraWrite tech is used in current SandForce controllers, but receives some updating and tweaks in this new controller. The latest version apparently offers improved data compression and garbage collection routines, as well as better block selection. All of these improvements would further decrease the rate of wear on the NAND flash itself over the lifespan of the drive.
SHIELD is the name given to LSI’s new error correction engine. All solid-state drives already utilize some proprietary versions of error correction, but SHIELD takes a different route. The ECC algorithm will monitor the NAND’s health by the rate of errors it detects, but as the NAND ages it will begin allotting additional over-provision capacity towards increased ECC protection. In effect, the ECC protection will allow for full performance early on in the drive’s lifespan, then at the point errors begin to increase it will switch to sacrificing a small amount of performance for increased data protection.
Admittedlym SandForce’s reputation is not the shiniest one around, however with LSI’s expertise in the enterprise storage and RAID markets the SF-3700 has a very strong promise of restoring the SandForce name. Given the incredible flexibility of the SF-3700 controller family we can expect to see third generation SandForce products proliferating quickly as next summer approaches, nearly three years after the launch of the SF-2200. Performance is mentioned to have improved as well, but unfortunately any specific numbers will have to wait until then!