Question Sandisk / WD IX SN530 Odd Storage Sizes (85GB, 170GB, 340GB)

[htwingnut]

These are "industrial grade" SSD's: https://shop.sandisk.com/en-se/products/ssd/internal-ssd/ix-sn530-nvme-ssd?sku=SDBPNPZ-340G-XI

Tom's Hardware even did a quick review of these SSD's here (all the way back in 2020!): https://www.tomshardware.com/news/w...to-industrial-grade-m2-ssds-with-the-ix-sn530

They are offered as either TLC 256GB, 512GB, 1TB, 2TB but also as SLC at 85GB, 170GB, and 340GB.

I am wondering about the odd sizes of the SLC. Since they are SLC, each NAND cell can store 2^1 = 2 data states, either 1 or 0.

TLC can store 2^3 = 8 data states: 000, 001, 010, 011, 100, 101, 110, 111

So it's 4x as much data, albeit with less endurance and performance.

2TB TLC would be 2048/4 = 512GB SLC, 1TB = 256GB SLC, 512GB = 128GB SLC

Even with over-provisioning that would be a hell of a lot of OP, like 33%.

I thought maybe they were a combination of chips, i.e. 340GB would be 256GB + 128GB = 384 ~ 12% OP. But not sure why they'd do that, especially when the TLC have no additional OP.

I can't find any information as to what NAND chips are used on this thing and how they arrive at those non-traditional capacities.

Is anyone familiar with how/why these are the capacities they offer?

 

[fzabkar]

They're dividing the capacity by 3. Effectively, 3 x TLC cells become 1 x pseudo-SLC cell.

 

[htwingnut]

They're dividing the capacity by 3. Effectively, 3 x TLC cells become 1 x pseudo-SLC cell.

Thanks. But TLC is 2^3 or 8 total states, where as SLC is 2^1 or 2 total states, so why isn't it 4x the difference? But what you say does make sense 85x3 ~ 256GB, 170x3 ~ 512GB, 340x3 ~ 1024GB