A Closer Look at OCZ Agility 4 SSD
OCZ seems to be about to cut all its ties with SandForce. The company has replaced each of its SandForce-based series: the fourth-generation Vertex and Agility series only employ Everest 2 controllers which are provided to OCZ by its own developer Indilinx using some technologies from Marvell. We wouldn’t say that it’s a better or equivalent replacement just because the SandForce and Indilinx solutions have different sets of highs and lows, yet OCZ clearly has no future plans for SandForce.
Thus, the Agility 4 series is targeted at the bottom market segment and priced comparably to Agility 3 and other SSDs with SF-2281 controllers and asynchronous flash. In other words, the price is going to be lower than the psychological 1$ per 1 gigabyte. This can only be achieved by using inexpensive flash memory, so the Agility 4 series obviously contains asynchronous MLC NAND flash, too. Compared to the Vertex 4 series with its Everest 2 controller and synchronous flash with ONFI 2.2 interface, the Agility 4 design formula includes the same Everest 2 controller together with asynchronous flash with ONFI 1.0 interface.
The Everest 2 controller using no data compression, the formal specs of the Agility 4 series are far from impressive.
In fact, they are inferior to those of the Agility 3 SSDs. The overstated specs of SandForce-based SSDs now play a nasty trick on the marketing folk as they struggle to explain customers why the Agility 4 series is better than its predecessor. However, you should be aware that the new specs are much more true to life because the promised speed can be achieved with any type of data and under fewer limitations.
One more consequence of not using SandForce controllers is the shorter product range in terms of storage capacity. The SandForce supports asymmetric distribution of flash memory among its channels, but the Everest 2 controller requires the same number of NAND devices on each channel. Therefore, 192 or 384-gigabyte versions of Vertex 4 and Agility 4 SSDs are not possible.
We’ve got two midrange models, with capacities of 128 and 256 gigabytes, out of the Agility 4 series for us to test.
These SSDs are shipped in the traditional packaging of OCZ’s entry-level products. Instead of a cardboard box, they come in a transparent plastic blister wrap. A paper insert provides some scanty product-related information. There are no specifications here. You can only see the logo of the series, a few marketing slogans and the product's part number.
There are no accessories just because there’s no room for them inside this packaging. The Agility 4 is an entry-level product, so you have to purchase any extras, such as an adapter to install it into a 3.5-inch bay, separately.
Typically of OCZ products, the SSDs have a case that consists of a metallic bottom and a soft plastic top. There is a sticker with the series name on the top of the SSDs. As you can see, the distinguishing color of the Agility 4 series is green. There's a more informative label on the bottom of the case. At least it shows you the capacity of the disk.
The PCBs of our Agility 4 SSDs are in fact identical to those of the Vertex 4 series. OCZ must have saved on developing yet another hardware design from scratch. They just use asynchronous instead of synchronous memory.
Just take a look at the PCBs of 256 GB Vertex and Agility 4 disks:
We can only see some discrepancies in their component layout but on both PCBs an Indilinx IDX400M00-BC controller is accompanied by a DDR3 SDRAM cache of the same capacity and speed. It is 512 megabytes (in two 256 MB chips) of DDR3-1333 SDRAM with a CAS latency of 9, even though the actual chips come from two different brands. Thus, the type of flash memory is not just the main but the only difference between the Vertex 4 and Agility 4 series on the hardware level.
The Agility 4 256GB contains 16 flash memory chips Micron 29F128G08CFAAA with asynchronous ONFI 1.0 interface. Funnily enough, we've seen the same chips in Agility 3 SSDs, so we can trace some consistency here. Each chip is 128 gigabits in capacity and contains two 25 nm flash memory dies. So, despite the limited bandwidth of asynchronous flash, the eight-channel Everest 2 controller installed in this Agility 4 disk can employ 4-way interleave, which may partially mask the low performance of the NAND devices. By the way, it is due to this interleave technique that the Agility 4 SSDs get faster as their capacity grows.
The 128 GB version has the same internals as the 256 GB one.
This might be expected since it has the same PCB, controller and cache memory (512 MB of cache, just like in the 256 GB model). Its flash memory is represented by 16 chips Micron 29F64G08CBAAA. Again, this is typical asynchronous flash we are familiar with by inexpensive SandForce-based products. Each chip is 64 gigabits in capacity and contains a single 25 nm MLC NAND flash die, so the Everest 2 controller can only use 2-way interleave on each channel in the Agility 4 128 GB.
The Agility 4 differs from the Vertex 4 series in firmware as well. The differences are few, though. Both series use the same basic firmware and get firmware updates concurrently. Consequently, their behavior is similar in certain ways. For example, the problems we discussed in our Vertex 4 review can be observed with firmware 1.5 for Agility 4, too. We mean the unstable sequential read speed and the temporary reduction in write speed when more than 50% of the disk capacity gets filled with data.
OCZ offers the Toolbox utility for working with all its SSDs based on the first- and second-generation Everest platform. It helps update firmware, view the S.M.A.R.T. attributes and perform a Secure Erase command.
The Agility 4 series comes with a 3-year warranty, as opposed to the 5-year warranty provided for Vertex 4 SSDs. This is yet another consequence of the low-end positioning, but the good news is that the Agility 4 disks costs about 15-20% less than their Vertex 4 counterparts.