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OWC Mercury Electra 6G 960GB SSD: Zeroes vs Incompressible
Incompressible data and SSDs
To increase the lifespan of the flash memory, Sandforce-based SSDs compress data and this impairs write performance as seen in the tests with the OWC Mercury Extreme Pro 6G; data compression in an SSD reduces write performance when the data is incompressible (JPG, compressed PSD or TIF, most video, encrypted data, etc).
But the OWC 960GB Mercury Electra 6G SSD is not Sandforce based.
According to OWC, it uses a Silicon Motion controller optimized for Mac (but also benefits PC) that specifically addresses Mac aspects with tuning and design to avoid TRIM issues/dependencies. The 960GB model also benefits from internal DRAM and copious flash to handled difficult write loads.
disktester fill-volume --xfer 128M --pattern randomblock
As can be seen, incompressible data exerts essentially no penalty—fantastic!
Write/read zeroes: 365 / 393 MB/sec
Write/read incompressible: 362 / 393 MB/sec
Note that the top speed is limited by the Thunderbolt to SATA chipset. Theoretical max is 400 MB/sec per lane, but there is always a little latency and overhead. So 393 MB/sec is excellent for this type of device (e.g., 4-bay Thunderbay Mini).