WD mixes TLC and QLC NAND in SN5000 gumstick product line

Western Digital’s Blue SN2000 gumstick SSD updates the existing SN580 TLC NAND product and adds a 4TB capacity variant by using QLC flash with a newer process technology.

The Blue SN580 is an M.2 2280 format PCIe 4 drive with 250GB, 500GB, 1TB and 2TB capacity levels built using BiCS5 112-later 3D NAND in a 3bits/cell (TLC) process, and sold as a consumer drive, not OEM. Its companion SN570 OEM drive, with the same capacity levels but using PCIe 3 not PCIe 4, used the same BiCS5 NAND and was replaced by the SN5000S.  

This SN5000S used BiCS 162-layer NAND organized in QLC (4 bits/cell) fashion and with 512GB, 1TB and 2TB capacity points. WD has not taken the same approach in the SN580 to SN5000 transition, opting for TLC BiCS5 flash for the 500GB, 1 and 2TB capacity points but BiCS6 162-layer QLC NAND for the upper 4TB capacity point.

This means that the SN5000 line has two controllers, one for the three BiCS5 TLC variants and a second for the 4TB BiCS6 QLC product. Both SN5000 variants are PCIe 4 drives, like the SN580.

A table summarizes the drive characteristics and maximum performance levels: 

This simple picture is deceiving though where the SN5000 is concerned. A look at the detailed performance numbers from the datasheet show how the SN5000 model’s performance varies with capacity and NAND type:

The random read IOPS start at 460,000 foir the 500GB model, peak at 730,000 for the 1TB product and then decline to 650,000 at 2TB but rise to 690,000 at 4TB, with the TLC-to-QLC and BiCS5-to-BiCS6 changeover. The random write IOPS also change with the switch, from 770,000 to a much higher 900,000 with the 4TB model.

The sequential write bandwidth also shows an inconsistent pattern: 4GB/sec at 500GB; 4.9GB/sec at 1TB; 4.85GB/sec at 2TB; and 5GB/sec at 4TB. Sequential read bandwidth is less variable and increases slightly with capacity, progressing from 5GBsec to 5.5GB/sec.

Endurance in terabytes written terms increases in a simple way with capacity: 500GB – 150TBW; 1TB – 300TBW; 2TB – 600 TBW and 4TB – 1,200 TBW.

WD has set Blue SN5000 prices at: 500GB – $69.99, 1TB – $79.99, 2TB – $139.99 and 4TB – $279.99. Download a datasheet here.