The Western Digital WD Blue SN500 SSD Review: Moving The Mainstream To NVMeby Billy Tallis on April 19, 2019 9:30 AM EST
Western Digital's mainstream consumer drives have long been branded as WD Blue drives, and this carried over to SSDs after their acquisition of SanDisk. The first two generations of WD Blue SSDs were SATA drives using TLC NAND and were worthy competitors for the Crucial MX series and Samsung 850 EVO. The WD Blue SN500 is the third generation WD Blue SSD, and it moves the WD Blue brand over to a very different market segment: the SN500 is an entry-level M.2 NVMe drive.
Western Digital has been selling consumer NVMe drives for a few years using their high-end WD Black branding, but NVMe isn't just for enthusiast products any more. For the past year we've been seeing most SSD brands offering a lower tier of NVMe products that sit between their SATA and high-end NVMe offerings, both in terms of price and performance. This entry-level NVMe niche has at times been squeezed down to almost nothing when there are particularly well-priced high-end drives, but the general idea of splitting the consumer NVMe SSD market into two tiers isn't going away. SATA is starting to be phased out of use for primary storage in client PCs. Western Digital started supporting that trend over a year ago with the PC SN520 SSD for OEMs, which the WD Blue SN500 is derived from.
|WD Blue SN500 Specifications|
|Capacity||250 GB||500 GB|
|Form Factor||M.2 2280 Single-Sided|
|Interface||NVMe PCIe 3 x2|
|Controller||Western Digital in-house|
|NAND||SanDisk 64-layer 3D TLC|
|DRAM||None (Host Memory Buffer not supported)|
|Sequential Read||1700 MB/s||1700 MB/s|
|Sequential Write||1300 MB/s||1450 MB/s|
|4KB Random Read||210k IOPS||275k IOPS|
|4KB Random Write||170k IOPS||300k IOPS|
|Power||Peak (10µs)||5.94 W||5.94 W|
|PS3 Idle||25 mW||25 mW|
|PS4 Idle||2.5 mW||2.5 mW|
|Current Retail Price||$52.99
Despite bearing the WD Blue name, the SN500 is functionally not a direct replacement for the SATA WD Blue SSDs. The SATA predecessors offered capacities up to 2TB, while the SN500's only capacity options are currently 250GB and 500GB. Those are the most common and important capacity points for consumer SSDs, but the absence of 1TB and 2TB options are a glaring omission, especially now that 1TB drives are approaching $100. The lack of high-capacity versions of the SN500 make sense when considering the OEM SN520 it is based on: that drive was intended to compete against the smallest form factor SSDs used tablets and the thinnest notebooks. The OEM SN520 is available in form factors as small as M.2 2230, and even though the retail SN500 uses the more typical 80mm length that offers the broadest compatibility with consumer systems, it retains the same layout that puts all the electronics in the first 30mm of the card. The SN500 uses a design that was never intended to accommodate more than 512GB of flash. The extra length on the card is occupied only by the drive's label.
Like many entry-level NVMe SSDs the SN500 uses only two PCIe lanes for its host interface, which ensures it cannot match the peak performance of high-end drives with PCIe x4 connections. The lower lane count helps keep the pin count and power consumption of the controller down, which are important factors for a M.2 2230 drive but matter considerably less for a retail drive like the SN500.
The other major compromise in the SN500's design is that it does not feature a DRAM buffer for caching the mapping tables for translating logical block addresses (LBAs) into physical memory addresses. A DRAMless SSD usually has significantly lower performance than a mainstream drive with enough DRAM to store the mapping information for the entire SSD. In the NVMe world, the Host Memory Buffer feature allows SSDs to borrow a small amount of the main system RAM (usually a few tens of MB) for this purpose, offsetting the performance loss that DRAMless SATA drives cannot avoid. Western Digital chose not to use the Host Memory Buffer (HMB) feature for the SN500 and SN520, instead opting to include a few MB of memory in the controller itself, but nowhere near the 256MB or 512MB that would be included on drives with discrete DRAM chips.
Aside from those two limitations, the SN500's controller shares the same basic architecture that the WD Black SN750's controller uses. Western Digital designed this architecture to scale across a wide range of products, so the cut-down configuration we find on the SN500 was part of the plan all along. These are the first generation of in-house NVMe controller designs from Western Digital, but based on our experience with the WD Blacks it doesn't feel like a 1.0 product: they skipped over all the disappointments that Silicon Motion and Phison had with their first NVMe controllers, and instead the WD Black went toe to toe with Samsung's NVMe SSDs. The WD Blue SN500 won't be setting any performance records with just a PCIe x2 interface, but it does have the opportunity to continue the impressive track record on power efficiency that Western Digital has been building.
The WD Blue SN500 may be a bit low-end by NVMe standards, but its performance specifications are still far above what SATA SSDs can provide. The SN500's write endurance rating of 0.3 DWPD over a 5-year warranty is standard for mainstream and many high-end SSDs. The current retail pricing is about 10-15% higher than the good deals on mainstream SATA SSDs of comparable capacity, so Western Digital is only charging a small premium for delivering NVMe performance. There are other DRAMless NVMe SSDs and some QLC-based NVMe SSDs on the market that are cheaper than the WD Blue SN500, so the new WD Blue has to do more than just outperform SATA in order to be competitive.
|AnandTech 2018 Consumer SSD Testbed|
|CPU||Intel Xeon E3 1240 v5|
|Motherboard||ASRock Fatal1ty E3V5 Performance Gaming/OC|
|Memory||4x 8GB G.SKILL Ripjaws DDR4-2400 CL15|
|Graphics||AMD Radeon HD 5450, 1920x1200@60Hz|
|Software||Windows 10 x64, version 1709|
|Linux kernel version 4.14, fio version 3.6|
|Spectre/Meltdown microcode and OS patches current as of May 2018|
- Thanks to Intel for the Xeon E3 1240 v5 CPU
- Thanks to ASRock for the E3V5 Performance Gaming/OC
- Thanks to G.SKILL for the Ripjaws DDR4-2400 RAM
- Thanks to Corsair for the RM750 power supply, Carbide 200R case, and Hydro H60 CPU cooler
- Thanks to Quarch for the XLC Programmable Power Module and accessories
- Thanks to StarTech for providing a RK2236BKF 22U rack cabinet.
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DyneCorp - Sunday, April 21, 2019 - linkYou got the EX920 512GB on sale. That's not the typical retail price, and the SN500 is already sitting at $65 retail.
You understand the price of this drive will go down? As they always do after initial release? And when the prices of NAND skyrocket again, the SN500 will have a major advantage?
For the majority of consumers, the SN500 is a viable option.
airider - Friday, April 19, 2019 - linkThis is WD clearing out their inventory while making way for the higher capacity/performance versions coming out shortly. Don't expect to see this product anymore by the end of 2019.
flyingpants265 - Saturday, April 20, 2019 - linkWait, so it's not QLC nand? That's great. It states 300TB write endurance, compared to the 100TB of the 500gb Crucial P1, for the same price. Goodbye, QLC! For now..
DyneCorp - Sunday, April 21, 2019 - linkFor consumers, the endurance rating matters none. You'll never chew through 100TB of endurance, especially under consumer workloads. The massive SLC cache buffers utilized in the P1 and 660p in addition to smart caching algorithms increase endurance substantially. Also, the DRAM buffer in addition to smart controller firmware effectively mitigate write amplification by several factors. You'll never chew through the endurance of the P1 or the 660p, period.
Endurance ratings are meaningless under consumer workloads. SSDs far outlast their given endurance ratings.
flyingpants265 - Wednesday, April 24, 2019 - linkWell, hopefully. Because just to download install one game (hitman 2) requires about 240GB of writes. If I do that 3 times, that's 1% of my drive's life gone.
flyingpants265 - Wednesday, April 24, 2019 - linkUh, 4 times.
DyneCorp - Wednesday, April 24, 2019 - linkThis is incorrect. 240GB of writes does not equal 240GB of endurance lost, especially if they are sequential writes because:
1.) The controller can reduce write amplification by intelligently shifting data around
2.) Sequential writes to the SLC cache increase endurance significantly
3.) Folding blocks from the pSLC cache to QLC actually increases endurance
DyneCorp - Wednesday, April 24, 2019 - linkBy the way, this is evidenced by the ADATA SU800. It has a massive dynamic SLC cache buffer and older Micron 32-layer 384-Gbit NAND and still carries the highest endurance rating on the market.
willis936 - Saturday, April 20, 2019 - linkI'm surprised there isn't a significant difference in idle power consumption or drive-side efficiency for a DRAMless NVMe drive. This is a pretty nice piece of hardware, regardless of price.
DyneCorp - Saturday, April 20, 2019 - linkThanks for the review, Billy! I really appreciate your work; you always do an excellent job and I appreciate you taking time out of your life to throw these reviews up.
Without the DRAM buffer, how do you think write amplification is affected? Obviously endurance is actually quite high (in SU800 territory) and performance is quite high. This is especially interesting considering how small the SLC cache buffer is.
Do you think WD has effectively mitigated negative endurance impact through firmware?