Adata's XPG SX300 family is the mSATA-based relative of the company's 2.5" SX900 line-up, which we covered in Time To Upgrade: 10 SSDs Between 240 And 256 GB, Rounded Up. They both employ SandForce's second-generation controller, suggesting that we may just see the compact form factor serving up performance similar to what we've been enjoying on the desktop for more than two years now.
In reality, the XPG SX300s are a little different than the most conventional SandForce-based drives. Like the SX900s, Adata takes advantage of a vendor update from the controller company that allows it to disable over-provisioning entirely. In our review of the SX900, we saw that over-provisioning helps the drive recover performance when all of its cells are written to. Getting rid of the feature can affect speed then, under the right conditions.
You'll notice that the XPG SX300s (all three of them, at 64, 128, and 256 GB) host four BGA memory packages, each of which connects to the controller via two channels. Thus, all three mSATA-based SSDs communicate over eight available channels. Adata tells us that it's using 25 nm synchronous flash from IMFT, which should enable impressive performance.
Why is there so much difference between the three versions in our 4 KB random read test, then? At the low queue depths you'd expect to encounter on an Ultrabook or mainstream desktop, the drives are actually fairly close together. It's only at queue depths of eight and more that the 256 GB model really takes off. This is a result of the interleaving that takes place as more NAND devices are involved in a given operation. At high queue depths, the larger SSD is able to better-utilize the interface between SandForce's controller and the attached flash.
Writing compressible information to the XPG SX300s (in the chart below) doesn't leave any room for interleaving to help performance. SandForce's DuraWrite technology helps all three SSDs achieve similar results.
However, we know that SandForce's architecture doesn't handle compressed data as elegantly. So, the 128 and 256 GB drives serve up notably better performance than the 64 GB model, which is composed of few NAND die. Moreover, the trio's benchmark numbers are significantly lower when each drive is forced to contend with incompressible information.
Sequential read performance is notably better. All three drives post similarly-impressive throughput, sailing over 500 MB/s at a queue depth of two.
So long as you're dealing with compressible data, 128 KB sequential write performance is also really impressive.
The impact of interleaving is profound once we force these mSATA-based SSDs to cope with purely incompressible information. The 128 and 256 GB models fall to 200 MB/s, while the 64G GB drive drops to 100 MB/s. Moreover, higher queue depths do nothing to improve transfer rates, since the architecture is already saturated at a queue depth of one. Stacking more operations only yields better performance when there's still headroom available.