TRIM Performance:
While SSD's offer many benefits, there are some downsides to using flash memory. One of the biggest issues people run into is performance degradation. Over time, an SSD will run out of fresh blocks and will have to write over data the file system has marked as deleted. This procedure is very complicated and can slow an SSD's write speeds considerably.
To fix this problem, most manufacturers have added TRIM support to their SSDs. The TRIM command allows an operating system, such as Windows 10, to tell an SSD which data blocks are no longer in use. Using this information, the drive pro-actively erases these blocks and adds them to the free block pool.
To test the WD_BLACK SN850's TRIM and garbage collection functions, I first put the drive in a "dirty" state. I used Iometer to fill 80% of the drive and then ran a random write test for 30 minutes. Looking at the screenshot below, you can see that the WD_BLACK SN850's average read and write speeds dropped to 4760.27 MB/s and 477.08 MB/s, respectively.
WD_BLACK SN850 - Dirty
To see how well the WD_BLACK SN850 could recover, I let the computer sit for about 30 minutes and then reran the test. The drive wasn't able to reach the factory fresh performance shown in our earlier tests. However, its sequential write speed climbed up to 743.12 MB/s.
WD_BLACK SN850 - After TRIM
Lastly, I used Parted Magic to perform a secure erase on the WD_BLACK SN850. With the drive wiped clean, it had average read and write speeds of 5632.23 MB/s and 4984.57 MB/s, respectively.
WD_BLACK SN850- Secure Erased
Final Thoughts:
Western Digital has clearly put a lot of time and effort into their new WD_BLACK SN850 SSD. In an effort to deliver the full potential of next-gen PCIe Gen4 technology, everything, from the WD_BLACK G2 controller to the 96-layer BiCS 3D TLC NAND flash, has been developed in house. Needless to say, this effort has paid off in spades as the WD_BLACK SN850 is one of the fastest consumer SSDs currently available. The 1TB version of the drive screamed through our sequential transfer rate tests, reading at speeds as high as 7,071 MB/s and writing at more 5,300 MB/s. It also did very well in our random write tests, producing nearly 211,000 IOPS at low queue depths.
The WD_BLACK SN850 is available now without the heatsink in 500GB, 1TB and 2TB capacities. Prices on Amazon.com currently range from $150 up to $450, with the 1TB version reviewed here retailing for about $230. The heatsink equipped models are expected to be available in early 2021 and will cost about $20 more.
Highs:
- Available in 500GB, 1TB and 2TB capacities
- PCIe 4.0 x4 interface with NVMe protocol
- Equipped with 96-layer BiCS3 3D TLC NAND
- Excellent sequential and random read and write speeds
- Small M.2 2280 form factor
- Large DRAM cache
- Available with or without RGB-enabled heatsink
- WD_Black Dashboard software with "gaming mode"
- 5 year warranty
Lows:
- Write speed drops considerably when SLC cache is full
- Can run hot under heavy workloads
- Does not support hardware based encryption
- Pricey
