[timbre1234]

The problem with this is that erase-to-program delay is a major factor in bad write quality.....you really don't want to erase a block and wait a long time before programming it. Where "long" is subjective and there are a lot of details here but the general rule is that the longer you wait after an erase to write, the less accurate your write is (colloquially, your zero decays as it sits)......so in practice while you do erase-ahead, you don't erase too far ahead of your writing and you certainly don't erase at TRIM time in most cases.

[avianlyric]

Didn’t know that. Don’t suppose you’ve got any links that describe the physical process that results in the correlation between write quality and erase-to-program delay?

[timbre1234]

Do you want research or do you want an analogy? I can give you both. On the research front:

    "An Experimental Analysis of Erase-to-Program Interference in Multi-Level Cell NAND Flash Memories" by F. X. Zhang, et al., in IEEE Transactions on Electron Devices, vol. 63, no. 4, pp. 1621-1628, April 2016.

    "Erase-to-Program Disturbance in NAND Flash Memory: Characterization, Modeling, and Mitigation Techniques" by M. H. Kim, et al., in IEEE Transactions on Very Large Scale Integration (VLSI) Systems, vol. 25, no. 9, pp. 2381-2392, Sept. 2017.

    "A Study of Erase to Program Disturbance in 3D NAND Flash Memory" by T. Wang, et al., in IEEE Transactions on Electron Devices, vol. 64, no. 7, pp. 3153-3159, July 2017.

    "Characterization and Modeling of the Erase-to-Program Disturbance in Multi-Level Cell NAND Flash Memories" by R. Micheloni, et al., in IEEE Transactions on Electron Devices, vol. 56, no. 11, pp. 2384-2392, Nov. 2009.

[avianlyric]

Don’t suppose you could still provide the analogy. It’ll probably make it easier for me to understand the research as I only have a basic understanding of the physics at play here.

[swagmoney1606]

How hard would it be to write custom firmware for an M.2 SSD?

I'm not even sure where to start

[avianlyric]

A good one? Extremely hard. Pretty sure 90% of and SSD firmware is just secret sauce magic to deal with the mess and noise the physical world creates when you try to cram so much entropy into such a tiny physical space.

[flangola7]

What do you mean less accurate? Data is binary. It either is or it isn't.

[avianlyric]

Data is binary when you writing software. There’s absolutely nothing binary about data when you’re in the messy world of electronics, where fundamentally everything is analog.

Reading data from multi-level flash chips, or from spinning rust, has more in common with an FM radio, or mobile phone radio, than it does with anything you’ll see in an IDE. It’s all very complex signal processing, trying to extract small signals from lots of noise, in that world you know what your data probably looks like. You then need checksumming to figure out if it’s correct, and if it isn’t you need to try again, or declare the data lost.