SanDisk Extreme PRO 480GB

The new Extreme PRO, however, as the name suggests, is centred on performance, targeting user groups such as gamers, enthusiasts and media professionals. The 480GB model comes in at just over £250, and we're looking at about 57p per formatted GB. While UK pricing for the Samsung SSD 850 PRO is yet to be confirmed, the MSRP of $400 in the US puts the 512GB model at around 60p per formatted GB. This means the two SSDs are very much in the same league of pricing, and given how well the SSD 850 PRO performs, it also means SanDisk very much has its work cut out for it.

Physically, the Extreme PRO has a plastic external chassis and fits the 2.5-inch, 7mm tall form factor – a spacer is provided for anyone using 9mm bays. PCI-E based SSDs are definitely the next big thing, but they're not her en masse yet, and as such this is another SATA 6Gbps model, and SanDisk has made no mention of any M.2 or mSATA versions of the Extreme PRO.

The Extreme PRO builds upon the design of the Extreme II – we never received an initial sample of said SSD but we have tested the 480GB model for this review so we can see the differences. As you can see, the new drive is available in three capacities, with SanDisk having abandoned the 128GB class model and introduced a 1TB class one. In terms of quoted performance figures, sequential read and writes are about the same as before. Peak random read performance has been upgraded by 5,000 IOPS, but the biggest difference is peak random write performance, which jumps from a maximum of 78,000 IOPS before to 90,000 IOPS across the board now, a 15 percent boost.

SanDisk Extreme PRO	240GB	480GB	960GB
Max Sequential Read (MB/sec)	550	550	550
Max Sequential Write (MB/sec)	520	515	515
Max Random Read - 4K QD32 (IOPS)	100,000	100,000	100,000
Max Random Write - 4K QD32 (IOPS)	90,000	90,000	90,000

SanDisk is sticking to a Marvell controller using its own custom firmware. The controller is the same as before, the eight-channel 88SS9187, but the firmware has been tweaked for greater performance consistency. Crucial has moved its recent drives (MX100 and M550) to the more modern 9189 controller, so it's interesting that SanDisk hasn't done the same, although there are apparently few differences between them.

The NAND used is also the same as before: SanDisk's own 19nm eX2 ABL MLC Toggle. Despite the fact that the Extreme PRO now has a 960GB model, SanDisk is sticking to 64Gb dies throughout the range. This means that even the lowest capacity drive has 32 NAND dies in total, which equates to four per controller channel. This is enough to saturate the controller channels, which is why we don't see a performance dip as capacity gets smaller. The final component is the cache, which is again repeated – in the 480GB model it's a Micron 512MB DDR3-1600MHz chip.

Opening the drive up, we find a basic single sided PCB with eight NAND packages in total, so there are eight 64Gb dies per package in the 480GB model. There are no capacitors to keep the drive powered on to protect data in case of power loss, though this is typically reserved for enterprise drives. The NAND, cache and controller are all cooled by thermal pads, and the drive will throttle its performance in case of overheating.

The Extreme PRO also sees the return of SanDisk's nCache Pro feature as part of its tiered caching system. As well as the volatile DRAM cache and the non-volatile MLC NAND, SanDisk allocates part of the NAND as an SLC cache, using some of the spare area gained from its over-provisioning. While there's no true power loss protection, part of the idea behind nCache is to get data into a non-volatile NAND area as quickly as possible to give it a higher chance of surviving power loss, and using the vast majority of the volatile DRAM cache solely for mapping the page table

The nCache accumulates small write commands so that they can be written as larger blocks to the MLC NAND – this improves performance since an SLC-style cache will be faster to write to than an MLC (as demonstrated by the TurboWrite feature of Samsung's SSD 840 EVO), and should also lead to less fragmented writes and lower write amplification too, thanks to it writing in larger blocks.

There are few other features to speak of. The Extreme PRO does have full support for DEVSLP, but it doesn't support the TGC Opal 2.0 or IEEE-1667 encryption standards. This is a shame, as it's something that's starting to become commonplace and that we're starting to expect as standard. It's also something that Samsung includes in the SSD 850 PRO.