The SanDisk Ultra 3D is probably an unexpected review for many because the drive has been on the market for quite a while. I'm only reviewing it because I recently had to buy a 4 TB 2.5" SATA SSD, and the SanDisk Ultra 3D ended up being my choice, mostly because of the affordable $400 price point. I couldn't find a decent review of the drive anywhere, especially none that list the TLC cache size and how much performance drops once pseudo-SLC is exhausted.

Synthetic performance of the SanDisk Ultra 3D is solid. Sequential speeds are pretty much all hitting the limit of the SATA 6 Gbps connection interface, and thus are very similar to other SATA SSDs. Random IO varies more between drives in this test group—the SanDisk Ultra 3D falls behind a bit and achieves results roughly in the middle of the SATA test group. Thanks to its DRAM cache, the drive's random write performance is better than some value-oriented M.2 NVMe SSDs, like the ADATA Falcon and ADATA Swordfish.

In terms of real-life performance, the Ultra 3D falls slightly behind some competing SATA drives. For example, the Samsung 860 EVO is 6% faster, and the Crucial MX500 5%. The fastest SATA drive we ever tested, the Seagate BarraCuda 120, is 6% faster, too. Compared to QLC-flash drives, the SanDisk SSD is around 20% faster, which is quite a lot. Modern M.2 NVMe SSDs are considerably faster than the SanDisk Ultra 3D. Budget NVMe SSDs are around 20% faster, and the best PCIe 4 drives extend that gap to over 40%.

For my use case, which involves copying a lot of game installations, I absolutely wanted to make sure the drive has good write performance, especially when the SLC write cache is exhausted. On all TLC and QLC SSDs, a portion of the NAND flash is operated in SLC mode to soak up incoming bursts of write activity. Writing to SLC is much faster than writing to TLC or QLC, but it does consume a lot of space because you're filling a memory cell designed to store 3-bits with just a single bit. For that same reason, I chose to avoid QLC drives, as QLC is extremely slow to write to once the SLC cache is full. Here, the SanDisk Ultra 3D can excel. The data suggests that it doesn't use SLC cache at all and writes to TLC directly, but at a speed that's high enough for it not to be an issue. With an average write speed of 441 MB/s to fill the whole drive, speeds are close enough to the SATA 6 Gbps interface speed limit. Other 2.5" SATA SSDs we tested reach similar speeds, though; examples are the Samsung 860 EVO 1 TB hitting 456 MB/s and Seagate BarraCuda 1 TB managing 460 MB/s. I can just assume that the 4 TB 860 EVO will perform the same, and the Seagate BarraCuda is not available in a 4 TB version.

As mentioned before, the SanDisk Ultra 3D is priced very competitively. At only $390 for a 4 TB drive, it is basically the most affordable 4 TB TLC SSD on the market. Some QLC-based models do go a bit cheaper, like $380, but as mentioned before, I specifically didn't want a QLC drive. When considering pricing, the only noteworthy alternative seems to be the WD Blue 4 TB priced at $390 right now due to a rebate. Normally, nearly all 4 TB SSDs are much more expensive, around $500 and up. For my use case, a SATA drive was sufficient, and pricing was more important, but if you have a spare M.2 NVMe slot in your system, definitely consider an M.2 SSD, too; they offer much higher performance than SATA drives, but are also more expensive. The only affordable option here is the ADATA SX8100 for $450 since everything else is priced north of $600.