Corsair's Force SSD Reviewed: SF-1200 is Very Good

SandForce takes a different approach. Instead of worrying about where to place a lot of data, it looks at ways to reduce the amount of data being written. Using a combination of techniques akin to lossless data compression and data deduplication, SandForce’s controllers attempt to write less to the NAND than their competitors. By writing less, the amount of management and juggling you have to do goes down tremendously. SandForce calls this its DuraWrite technology.









DuraWrite isn’t perfect. If you write a lot of highly compressed or purely random data, the algorithms won’t be able to do much to reduce the amount of data you write. For most desktop uses, this shouldn’t be a problem however.




Despite the obvious achilles’ heel, SandForce’s technology was originally designed for use in the enterprise market. This lends credibility to the theory that SandForce was Seagate’s partner of choice for Pulsar. With enterprise roots, SandForce’s controllers and firmware are designed to support larger-than-normal amounts of spare area. As you may remember from our earlier articles, there’s a correlation between the amount of spare area you give a dynamic controller and overall performance. You obviously lose usable capacity, but it helps keep performance high. SandForce indicates that eventually we’ll see cheaper consumer drives with less NAND set aside as spare area, but for now a 128GB SandForce drive only gives you around 93GB of actual storage space.

Introducing the SF-1200

The long winded recap brings us to our new friend. The Vertex 2 Pro I previewed last year used a full fledged SF-1500 implementation, complete with ridiculously expensive supercap on board. SandForce indicated that the SF-1200 would be more reasonably priced, at the expense of a performance hit. In between the two was what we got with OCZ’s Vertex Limited Edition. OCZ scored a limited supply of early controllers that didn’t have the full SF-1500 feature set, but were supposedly better than the SF-1200.









Today we have Corsair’s Force drive, its new performance flagship based on the SF-1200. Here’s what SandForce lists as the differences between the SF-1500 and SF-1200:

SandForce Controller Comparison
	SF-1200	SF-1500
Flash Memory Support	MLC	MLC or SLC
Power Consumption	550 mW (typical)	950 mW (typical)
Sequential Read/Write Performance (128KB)	260 MB/s	260 MB/s
Random Read/Write Performance (4K)	30K/10K IOPS	30K/30K IOPS
Security	128-bit AES Data Encryption, Optional Disk Password	128-bit AES Data Encryption, User Selectable Encryption Key
Unrecoverable Read Errors	Less than 1 sector per 1016 bits read	Less than 1 sector per 1017 bits read
MTTF	2,000,000 operating hours	10,000,000 operating hours
Reliability	5 year customer life cycle	5 year enterprise life cycle

The Mean Time To Failure numbers are absurd. We’re talking about the difference between 228 years and over 1100 years. I’d say any number that outlasts the potential mean time to failure of our current society is pretty worthless. Both the SF-1200 and SF-1500 are rated for 5 year useful lifespans, the difference is that SandForce says the SF-1200 can last for 5 years under a "customer" workload vs. an enterprise workload for the SF-1500. Translation? The SF-1500 can handle workloads with more random writes for longer.




The SF-1500 also appears to be less error prone, but that’s difficult to quantify in terms of real world reliability. The chip sizes are identical, although the SF-1500 draws considerably more power. If I had to guess I’d say the two chips are probably the same with the differences amounting to be mostly firmware, binning and perhaps fusing off some internal blocks. Maintaining multiple die masks is an expensive task, not something a relative newcomer would want to do.






Note the lack of any external DRAM. Writing less means tracking less, which means no external DRAM is necessary.




Regardless of the difference, the SF-1200 is what Corsair settled on for the Force. Designed to be a high end consumer drive, the Force carries a high end price. Despite it’s 100GB capacity there’s actually 128GB of NAND on the drive, the extra is simply used as spare area for block recycling by the controller. If we look at cost per actual GB on the drive, the Force doesn’t look half bad:

SandForce Controller Comparison
Drive	NAND Capacity	User Capacity	Drive Cost	Cost per GB of NAND	Cost per Usable GB
Corsair Force	128GB	93.1GB	$410	$3.203	$4.403
Corsair Nova	128GB	119.2GB	$369	$2.882	$3.096
Crucial RealSSD C300	256GB	238.4GB	$680	$2.656	$2.852
Intel X25-M G2	160GB	149.0GB	$489	$3.056	$3.282
OCZ Vertex LE	128GB	93.1GB	$394	$3.078	$4.232

But looking at cost per user addressable GB isn’t quite as pretty. It’s a full $1.12 more per GB than Intel’s X25-M G2. It's also a bit more expensive than OCZ's Vertex LE, although things could change once Corsair starts shipping more of these drives.