Closer Look at SanDisk Ultra Plus 256GB
The SanDisk Ultra Plus embodies some original solutions rather than copies the conventional architecture of the majority of SATA 3 drives. The controller uses fewer than eight channels to communicate with flash memory but the available channels are utilized more efficiently. This has helped make the SSD design simpler and cheaper and also reduce the power consumption of the resulting product. Of course, with fewer controller channels, the SSD is likely to perform slower, but SanDisk, being a flash memory maker, has some tricky technologies to make up for that.
To be specific, the SanDisk Ultra Plus is based on the Marvell SS889175 controller. We have not met any SSDs with this chip so far, just because it is not designed for consumer SSDs. It is a simplified version of the popular Marvell SS889187 controller, which is employed in such products as the Plextor M5 Pro and the Crucial M500, but with only half the memory access channels. The SS889175 is meant for mobile applications that do not require high performance, but SanDisk has found a new purpose for it.
The controller is coupled with SanDisk’s exclusive eX2 ABL MLC NAND flash memory manufactured on 19nm tech process. Similar to conventional synchronous MLC memory with Toggle Mode interface, it features the proprietary nCache technology: some of the MLC memory cells work in faster SLC mode and act as a nonvolatile cache to increase writing performance and improve service life since caching involves consolidation of fragmented requests.
Now that we have a general picture of the Ultra Plus’s architecture, let’s take a look inside the 256GB model we’ve received to test. Its PCB is surprisingly small, populated by very few chips, yet we can find all conventional components here.
First of all, the SanDisk Ultra Plus 256GB only has four memory chips. Each of them is 64 GB and contains eight 8-gigabit NAND devices, so the controller uses 8-way interleaving in this SSD. By the way, that’s why the SanDisk Ultra Plus series cannot include any models with capacities above 256 GB.
Besides the flash memory and the Marvell SS889175 controller, the PCB carries a dedicated DRAM buffer typical of any non-SandForce-based SSD. It is a 128MB chip of DDR2-800 SDRAM. Thus, considering the nCache technology, the SanDisk Ultra Plus does double caching. And it is this double caching that is expected to ensure high performance with the 4-channel controller. Theoretically, it should work because SLC memory is about twice as fast as MLC memory.
There’s only one questionable thing concerning the size of the nCache. The flash memory installed into the SanDisk Ultra Plus has standard organization, i.e. 8-gigabit semiconductor devices. The SLC cache is allotted from the drive’s total capacity and cannot have a large size. The user-inaccessible part of SanDisk Ultra Plus drives is a typical 7% or about 17.5 GB. Some of this reserved pool must be used for block replacement, garbage collection and wear leveling instead of nCache. Moreover, SLC memory needs twice the memory cells for storing data in comparison with MLC memory. All in all, it seems that the nCache is only about 4 GB large in the 256GB model. That’s not much. On the other hand, this should be enough for regrouping and accelerated execution of random-address requests, which is the main point of the technology according to SanDisk.
The manufacturer suggests that this SLC cache is enough to make the Ultra Plus as fast as modern SSDs with 8-channel controllers. This is indicated by the official specs of the SanDisk Ultra Plus 256 GB:
- Controller: Marvell SS889175;
- Interface: SATA 6 Gbps;
- Flash-memory: synchronous 19 nm Toggle Mode eX2 ABL MLC NAND;
- Size: 256 GB / 238 GiB;
- Cache-memory: 128 MB DDR2-800 SDRAM + SLC NAND nCache;
- Sequential read speed: up to 530 MB/s;
- Sequential write speed: up to 445 MB/s;
- Random read speed (4 KB blocks):820,000 IOPS
- Random write speed (4 KB blocks): 39,000 IOPS.
Of course, the relatively high speed is ensured not only by the dual caching but also by firmware optimizations. The latest version is X2306RL and we recommend using it since it has certain improvements and corrects earlier bugs.
Thus, the SanDisk Ultra Plus looks like a typical inexpensive SSD. Its hardware components don’t seem advanced, but it may be competitive in real-life applications. Its manufacturer positions it lower than the SandForce-based Extreme series, though, which is reflected in the way the Ultra Plus series is offered to the customer.
The packaging is rather dull. It is just a small gray box.
The SSD is shipped together with a user manual and a frame that can increase its thickness from 7 to 9.5 mm. You can also download the SSD Toolkit utility from the SanDisk website. The utility isn’t very functional but offers some basic features like viewing general info about the SSD, checking out SMART parameters and updating firmware.
The SSD case is made of robust plastic. The model can be identified by two stickers: a large gray label with logos on one side and an info sticker with part number, serial number and barcodes on the other.
Talking about the new drive’s positioning, SanDisk claims that the Ultra Plus is especially good for multimedia data and recommends it for image and audio editing applications. We’ll check this out in our tests.
Although the nCache technology is expected to improve the service life of flash memory, the SanDisk Ultra Plus comes with a standard 3-year warranty.