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1st tests of the Vertex 2 / SandForce SSD
has been able to get its hands on a pre-version of the Vertex 2 Pro SSD, an early vintage of the collaboration between OCZ and SandForce announced last November. This SSD won’t be commercially available before March. The first surprise is that SandForce doesn’t use any external DRAM but just the cache built onto the controller. The SSD has a large 90mF capacitor designed to make sure no buffered data is lost should there be a power out.
Performances in practice are very high with the Pro version, using the highest end controller, reaching sequential reads of 265 MB/s and sequential writes of 252 MB/s. For random reads of 4 KB blocks we’re at 51.3 MB/s (as against 38 MB/s with Indilinx and 64 MB/s with Postville) and writes at 50.9 MB/s (compared to 13.6 MB/s with Indilinx and 39.1 MB/s with Intel). In PC Mark Vantage this Vertex 2 Pro is 11, 18 and 46% faster than the Postville 80 GB and 160 GB and the Indilinx 128 GB.
To achieve such results, SandForce has developed DuraWrite technology which will lower write amplification under 1x! Remember, the write amplification is the ratio between the volume of data written on the flash memory (flash write) and the volume of data to write requested by the system (host write). Intel has highlighted the fact that it kept write amplification on its SSDs down to 1.1x. SandForce has announced 0.5x and says, for example, that installation of Vista and Office requires a total of 25 GB (host writes), but that in practice only 11 GB are written in Flash (a write amplification of 0.44x).
How is this possible? Obviously this isn’t bit-for-bit data storage and SandForce must have implemented compression and deduplication algorithms within the controller. Of course this technology will work less well with compressed data and write speeds for compressed data will drop to 145.9 MB/s according to AnandTech’s tests, which is in any case not bad.
Reducing flash writes is of course beneficial both in terms of write speeds and reliability as the number of write cycles is critical in terms of how long flash memory lasts. So as to limit wear on the flash, SandForce also includes additional extra internal information similar to RAID5 (without going into more detail) and makes it a point of honour to have a lot of additional flash: the first SSDs will be the 50, 100, 200 and 400 GB versions but they will actually have 64, 128, 256 and 512 GB of flash memory. These are the enterprise versions, with the standard versions having less additional space.
All in all a very promising controller then, although we would have liked to see SATA 6 Gbits/s support.
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