Articles: Storage

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Today’s consumer-class SATA 6 Gbit/s solid state drives are mostly based on MLC flash memory with synchronous interface. This type of memory helps make products with the most attractive price/performance ratio because, when connected to today’s eight-channel SSD controllers, it delivers a combined data-transfer rate comparable to the SATA 6 Gbit/s bandwidth. However, some manufacturers employ flash memory with asynchronous interface which is also supported by every modern SSD controller. Such memory is slow but cheap. The resulting products cost somewhat less and have much lower speed specifications, yet they do enjoy some demand. After all, an SSD with asynchronous flash is anyway much faster than any conventional hard disk drive.

Fortunately for SSDs with asynchronous MLC NAND flash, SandForce controllers compress data prior to writing this data onto the drive. Thanks to that, SandForce-based SSDs can make full use of the SATA 6 Gbit/s bandwidth even if equipped with asynchronous flash. Such SSDs can only deliver their maximum speed with compressible data but their manufacturers write these maximums into their specs anyway. This trick with specifications, which seem to be comparable to those of SSDs with synchronous memory, combines with the lower prices to help SSDs with asynchronous flash sell well. That’s why many leading SSD makers think it necessary to offer such products under their brand.

Due to the abovementioned reasons SATA 6 Gbit/s SSDs with asynchronous memory used to be based on the SandForce platform. For example, every SSD with a Marvell controller available now features synchronous flash only. However, the SandForce series has been losing its ground and many makers have been looking for alternative solutions, so now there appear SSDs with asynchronous memory, based on controllers that don’t do any on-the-fly data compression. One of the first of them was the OCZ Petrol whose asynchronous flash was managed by an Indilinx Everest controller. The Petrol didn't impress us much, though. It turned out to be slow and not very reliable. But it was just the first attempt and the manufacturer must have thought it more or less successful.

So today we are going to take a look at OCZ’s second attempt to combine asynchronous flash with a non-SandForce controller. Having upgraded its own controller to version 2 and tested it in the fairly good Vertex 4, OCZ now rolls out an entry-level product with the same design but asynchronous flash. The Agility 4 is in fact a cheap Vertex 4. However, like its predecessor, the Everest 2 controller has no technology to make up for the low bandwidth of slow asynchronous flash memory.

Having got two Agility 4 models of the most popular capacities (128 and 256 GB), we want to see if the slow flash and the fast Everest 2 controller can be mixed up to produce something worth our money.

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