Many PC owners use SATA connected
SSDs. They’re affordable, dramatically quicker than conventional hard drives and almost every computer built in the last ten years has the SATA III 6Gbit/s interface to connect them. But M.2 SSD drives with NVMe are now replacing SATA and the WD Blue SN550 is one of the best you can buy.
In modern systems they can offer up to six times the performance of the older technology. This switch might have happened more rapidly had NVMe modules been more affordable and come in bigger capacities like the WD Blue SN550 does.
Design & Build
M.2 NVMe drives are often deceptively complicated devices that combine flash modules, RAM cache and controllers on a tiny edge connecting board.
What’s interesting about the SN550 is how uncomplicated WD engineers managed to make it, with very few tracks on the underside of the board and all the discrete electronics on the top. Often NVMe makers obscure the source of parts on the PCBs to enable them to change suppliers or specs more easily.
But here the 3D NAND chip top clearly shows its SanDisk origin, a company that Western Digital bought in 2016 for a mere $19 billion.
A single TLC NAND chip that contains sixteen 512Gb dies provided the whole 1TB for the review drive. And, this begs the obvious question as to why there isn’t a 2TB or even a 4TB option? There is certainly enough space on the board to mount the extra chips.
One answer might be that heat would be an issue, as the NAND and controller chip are at opposite ends of the PCB. But there are no heat spreaders or sinks on any of the chips, so it isn’t the whole story.
The controller is an in-house design and includes an NVMe 1.4 interface to access four lanes of PCIe, double the bandwidth used by the previous SN500. Where the design diverges from the norm is that it doesn’t use DRAM or a host memory buffer to balance the available bandwidth against the real speed of the 3D NAND.
Instead, the custom controller has a small amount of SRAM that performs this function.
One notable omission is that this drive has no hardware encryption, making it unsuitable for those businesses that insist on locking down their computers entirely. This requirement is mostly an issue that impacts business users, and you can still use software encryption like BitLocker Go, but it’s one of the features that more expensive NVMe drives offer.
For good reason, those who rely on SSDs to keep their files from no longer existing can be sensitive about the life expectancy of these storage devices.
The endurance of the SN550 depends on the capacity chosen, and the 250GB model has 150TBW, doubling to 300TBW for the 500GB drive and 600TBW for the 1TB model.
We can’t realistically test the validity of these numbers, of course, but Western Digital has a five-year warranty, and that would equate to the user writing 328GB of data every day for that entire period to hit the TBW limit on the 1TB model.
The 150TBW level on the 250GB drive is probably another good reason not to buy that one, even if that still has the equivalent 80GB per day of writing for five years to, in theory, wear it out.
In short, unless you write huge amounts of new data every day, and delete almost as much, the lifespan of the SN550 isn’t likely to be an issue for most users for at least five years or realistically much longer.
It isn’t a secret, but most flash drives have a performance limit that is generally hidden from the user by the elegant application of caching. The SN550 isn’t any different, and part of our testing is to determine the point at which the cache in the operating system and on the drive becomes saturated, revealing the true underlying flash speed.
But before we talk about that, the quoted performance for the 1TB model are 2400MB/s for read and 1900MB/s write. And testing this assertion using CrystalDiskMark 7, the SN550 achieved those numbers with a little extra to spare.
Other benchmarks offer slightly lower numbers, often for reading, but didn’t undermine the quoted performances in any significant way. The only place this drive suffers is when the write request queue is long, and it appears to bottleneck more than we’ve seen on other drives, like the Samsung 970 EVO.
The likelihood of running into these caveats is dependent on the usage profile of the system, and for most users, this idiosyncrasy is unlikely to be an issue.
As with all drives that use flash modules, once the cache is full, the transfer will slow down to about 800MB/s. On the 1TB model this threshold is around 12GB, so copying a file larger than this to the drive (from another NVMe drive) will progress quickly until you hit this value and then decline to around 800MB/s until finished.
The sustainability of write performance is an issue for all flash-based designs, and the only means to elevate it is greater amounts of cache. But, as this is designed as a cost-effective solution, and wasn’t intended to win any speed race, that wasn’t an option here.
Other drives can handle sustained writing better, but the SN550 isn’t bad and much better than the prior SN500 design and other cheap NVMe options.
Western Digital has three capacities of SN550 SSD available with 250GB, 500GB and 1TB options.
These are all M.2 2280 form factor modules that are 80mm long, 22mm wide and less than 2mm thick. To use one you’ll need either an M.2 NVMe capable slot or a PCIe NVMe carrier card. And, to boot, you’ll need a motherboard with UEFI bios that can boot from PCIe devices.
The 1TB SN550 reviewed here can be found on
Amazon.com for just $149, and the smaller capacities are $54.99 and $46.99 respectively.
We suspect the elevated cost of the 1TB model is down to demand, and once the channel has sufficient stock, that price should drop closer to $100.
For those in the UK where stock is less of an issue, the 1TB option is £99.95, 500GB is £62.99, and the 250GB is just £44.67. You can find them on
Wherever you get it, the 1TB drive is undoubtedly the best value, and given the difference between them is so small, the 250GB seems a silly budget constraint to make.
From a price perspective, this matches the Crucial P1 1TB, is a little cheaper than the Crucial M500, Intel 660p and XPG SX6000 Pro. But it’s substantially less than the Kingston A200,
Samsung 970 EVO,
Corsair Force MP510 and
Western Digital’s Black SN750.
Some of these drives are faster than the SN550 but at more than 50% the cost they don’t offer the same value for money.
If you want ultimate speeds, especially in respect of writing, or hardware encryption then look elsewhere. The WD Blue SN550 is more of a family people-carrier than a head-turning roadster, to use a vehicle analogy.
That said, the benchmark numbers still make this substantially quicker than anything connected via SATA, and a significant improvement over the SN500 model that it replaces.
It doesn’t have the caching to handle very the intensive situations that data processing tasks and server demands, but for a desktop system it is more than adequately provisioned.
We’d avoid the 250GB capacity version for many reasons, but the 500GB and 1TB drives are a solid investment for anyone wanting to upgrade to NVMe storage cheaply.
Our only concern is that the demand for these drives could outstrip supplies quickly, considering that component might be impacted by issues beyond Western Digital’s control.
If you fancy a cheap NVMe drive upgrade, now is a great time to snag one of these.
chart of the best SSDs to see what other options there are and how we rate them.
WD Blue SN550: Specs
- Capacity: 250GB, 500GB and 1TB
- Interface: M.2 NVMe PCI slot (PCIe Gen3 up to 32 Gbps)
- Sequential speed read: 2400MB/s
- Sequential speed write: 950MB/s, 1750MB/s and 1950MB/s for 250GB, 500GB and 1TB drives
- Colour: Blue
- Dimensions: (L x W x H): 80 x 22 x 2.38mm
- Weight: 6.5g
- Warranty: 5 years