Results: Sequential Performance
Fantastic sequential read and write performance is a trademark of modern SSDs. To measure it, we use incompressible data over a 16 GB LBA space, then test at queue depths from one to 16. We're reporting these numbers in binary (where 1 KB equals 1024) instead of decimal numbers (where 1 KB is 1000 bytes). When necessary, we're also limiting the scale of the chart to enhance readability.
128 KB Sequential Read
Silicon Motion's platform comes out swinging. We're showing data from the last few 128 GB-class drives for comparison, and it looks like SanDisk's Extreme II 120 GB is the most similar. Perhaps that shouldn't be surprising, since both SSDs share Flash Forward's eX2 Toggle-mode NAND in common. Despite their different controllers (the Extreme II employs Marvell's 9187 eight-channel processor), both drives are nearly identical as we step through higher queue depths. Bear in mind the chart scaling; for better separation, the scale is limited.
128 KB Sequential Write
Keep in mind that the 120 GB 840 EVO and 120 GB M500 sport half as many dies as the other SSDs in this chart. Crucial's M500 plods along near 130 MB/s, which is where the EVO would be as well if it weren't for its emulated SLC write buffer. SanDisk's Extreme II and the Silicon Motion platform both peak around the same throughput, though the reference platform starts off lower with just one command in its queue. That could be explained by the four-channel design. SanDisk's Ultra Plus 128 GB slots in under Silicon Motion's sample.
Here's a break-down of the maximum observed 128 KB sequential read and write performance with Iometer:
Silicon Motion's drive finds shelter amongst a rash of mid-pack 256 GB drives. It may be too simplistic to say this, but SATA 6Gb/s-based SSDs using similar flash generally lay down similar sequential write speeds. This chart lends some evidence to that, though it's not universally true. Take the Vector, for instance. While writing up to half of the drive's capacity happens at or near 500 MB/s, the second half is written at 50% of that speed (in one sitting, at least). That's an example of clever and firmware tricks companies like OCZ are using to differentiate their products in a highly competitive environment.
The maximum read speeds reflect an astonishing lack of diversity. With most modern flash and the SATA 6Gb/s interface, you tend to see 500 MB/s+ ceilings. The m4 256 GB actually has the lowest sequential read speeds of this bunch, but it was quite a bit lower at launch. The bump up to 500 MB/s had a lot to do with the 0009 firmware update that changed the m4's initially mild-mannered nature. At least, that's how we remember it.