SanDisk Ultra Plus 256GB SSD Review
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SanDisk’s SSDs are rapidly gaining momentum after initially being one of the first to offer solid state storage directly to consumers. Since those early days they have consistently delivered drives known for their performance and value like the excellent SanDisk Extreme 240GB which turned out to be one impressive storage solution. On the other hand, the new Ultra Plus series has the same aims as its Extreme sibling but targets a slightly lower price point.
The $210 Ultra Plus 256GB is SanDisk’s big entry into a market which is currently filled with affordable alternatives which do a great job of combining price and raw power. For example, OCZ’s Agility 4, Kingston’s SSDNow V300 and the Neutron series from Corsair all play in the same ballpark as the Ultra Plus and have been on the market for significantly longer. So how is SanDisk planning on competing against industry heavyweights? By sure-footed innovation and a unique blend of components.
When putting specifications on the table, there really isn't much to distinguish the new Ultra Plus series from SanDisk's higher end Extreme SSDs. The main differentiating factors are write speed and the Ultra Plus' availability in lower capacity formats. It really makes us wonder how SanDisk is planning to market these two very similar drives.
With its value orientated approach, the semi-plastic and metal chassis comes shouldn’t come as a great surprise. It does however come in a slimming 7mm form factor and includes a plastic topper plate which converts the drive into a standard 9.5mm high form factor. This customizable approach makes the Ultra Plus perfect for a wide array of systems including some in which typical 9.5mm SSDs simply won’t fit.
By gently removing the plastic top half we can instantly understand how SanDisk were able to offer a large capacity SSD at such a reasonable price. It’s all about miniaturization. This is one of only a handful of drives which utilize such a small internal PCB, but unlike the Corsair Accelerator 30GB there are quite a few differentiating factors which allow this design to stand out.
Much like the Accelerator 30GB there are only four large capacity NAND ICs on this amazingly small PCB. However instead of ONFi 1 NAND, SanDisk has opted for four of their own new high performance 19nm eX2 ABL MLC NAND ICs.
eX2 ABL MLC NAND provides a unique twist on a typical MLC design since a portion of the NAND can act in pseudo 1bit SLC mode. The amount of space used in 1bit mode can be dynamically adjusted but in this instance it has been set very low. The only area which will run in pseudo SLC mode on the Ultra Plus is just the normal over-provisioning all NAND ICs come with at the chip level. This area is usually just used for bad block replacement – and ensures all chips meet minimum size specifications - but in this case it pulls double duty as a type of quasi cache storage, or what SanDisk calls called nCache.
nCache is a technique SanDisk has created to help improve overall write performance and boost sustained performance of their drives. It does this by taking a piece of the NAND, setting it to run in pseudo SLC mode and allowing the controller use this area much like a RAM IC.
Basically, the nCache area will act as a buffer for small file writes, garbage collection and the like. The controller can quite literally push small, time sensitive writes to the nCache, flush its RAM buffer and move on to other I/O requests without bogging down the system. Then the controller can periodically – during low I/O periods – consolidate these small writes to the MLC portion of the NAND. This also has the added benefit of increasing the lifespan of the NAND as fewer blocks will need to be used for the small files and thus fewer will need to be cleaned and consolidated.
The other noticeable difference here is the controller. Unlike the Sandisk Extreme which relies upon a SF2281, or the Corsair Neutron use of Link A Media Devices’ 'Amber' LM87800, the Ultra Plus makes use of the Marvell "Van Gogh Lite" 88SS9175-BJM2 controller.
The 9175 is a four channel design and has been optimized for lower power usage, making this drive an excellent fit for the notebook market. It also is much less expensive than the more powerful 9174 and this coupled with the low number of 19nm MLC NAND explains how SanDisk was able to keep the cost of the Ultra Plus low. Just like any Marvell controller there is also a single RAM IC, which in this instance is a Samsung 128MB DDR2-800 DRAM chip.
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