NAND Flash Faces Off - Synchronous vs. Asynchronous

News flash! All flash NAND is not created equal! Sure, you know about multi-level and single-level NAND when it comes to speed, but what about synchronous and asynchronous NAND inside your shiny new SSD? We have answers and tell you where your money is best spent for real data speed.


There is a lot of misinformation floating around the inner web tubes about the latest batch of solid state drives hitting the market. We wanted to help our readers get to the bottom of synchronous and asynchronous NAND in SandForce Solid States Drives and what it means to you.

Synchronous & Asynchronous

As you may know, manufacturers of SandForce based products are in the process of releasing two models of products based on the SF-2281 SATA III controller. These products differ by the type of flash used, ONFi 2.x synchronous and ONFi 1.0 asynchronous NAND flash. Without picking on any one manufacture we’ll toss out some examples; OCZ has the Vertex 3 and Agility 3, OWC has Electra, Mercury Extreme Pro 6G, and Corsair has the Force GT and Force 3 SSDs. The list is growing every week as new products pass through R&D and into retail.

Both flash types use a 25nm die package size. The technical term is ONFi 2.x (synchronous) and ONFi 1.0 (asynchronous). ONFi 2.x uses a central timing circuit and moves data on both the rise and fall of the signal wave. This is similar to double data rate random access memory (DDR RAM). ONFi 2.0 is capable of delivering speeds up to 133MB/s but ONFi 1.0 is limited to just 50MB/s. On paper it sounds like one is twice as fast as the other but due to the total SSD architecture the real world benefit is much less.

Devil is in the Details

Below we see two typical specification listings for two products from the same company that we have placed on the chart side by side for easy comparison. As you can see in the chart, both drives look like products that perform very close to each other and would be worthy of most power users.

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The reality is one of these products is excellent, the fastest SSD currently available on the market. The other is much slower in nearly all real world tasks. As you can see though this is not reflected in the specifications. We added the Storage Technology tab across the top; this information is generally hidden in the fine print.

There is an old saying, "Trust but verify." We expect manufacturers to market products the best it can but it is our job to verify and give accurate information. The blanket statement in most reviews these days is that asynchronous flash when paired with SandForce SF-2281 controllers only affects performance when dealing with incompressible data, or rather data that has already been compressed before it gets to the SandForce controller, such as .jpeg or .mp3 files. This is simply not accurate.

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The SandForce controller’s architecture is based in part on compressing data to increase performance. SandForce accomplishes this in a couple of ways but compression technology plays the largest role.

To say that an asynchronous flash drive is impacted only by incompressible data traffic just doesn’t cut it because all data is compressed by the time it is written to the flash. It doesn't matter if the data is compressed by file type (JPEG, MP3) or if compressed by the controller, everything written to the flash is compressed. The performance reduction can be as high as 60% but you wouldn’t know it from reading most of the reviews being published.