[pkaye]

The FTL is like a virtual memory manager. It is firmware/hardware to manage things like the logical to physical mapping table, garbage collection, error correction, bad block management. Yes there will be a lot of FTL data structures stored on the flash. It can be made durable by redundant copies, writing in SLC mode or having recovery algorithms. I used to develop SSD firmware in the past if you have further questions.

[jng]

Hey that's very interesting! How much of the FTL logic is done with regular MCU code vs custom hardware? Is there any open source SSD firmware out there that one could look at to start experimenting in this field, or at least something pointing in that direction, be it open or affordable software, firmware, FPGA gateway or even IC IP? I believe there is value in integrating that part of the stack with the higher level software, but it seems quite difficult to experiment unless one is in the right circles / close to the right companies. Thanks!

[pkaye]

Typically the Host and NAND interface have custom hardware. When the host issues a command, the hardware might validate it and queue up data to a buffer. On the NAND interface there might be a similar queue for NAND commands. You might have multiple queues for different priorities of operation. The error correct will also be in hardware. When you issues NAND reads and writes, the ECC will be checked or encoded. The rest of the FTL might all be in firmware. Perhaps a single core does everything. Or maybe its partitioned between two cores, one for the host related code and the other for the FTL related. Some companies have tried lots of cores, each with a dedicated state machine to handle some part of the operation. These can be complex to coordinate their operation and to debug. Some companies convert some of these state machines into custom hardware.

The only open SSD platform I've read about is http://openssd.io/ but I've never played with it. One of the challenges is the NAND manufacturers a lot of the critical documentation under an NDA these days. You really need that information to make a reliable SSD. When you learn how the internals of an SSD work, its a wonder that it retains data at all!

In terms of integrating SSD with the higher software level, I believe FusionIO was doing this in the past. They put the whole logical to physical mapping into the host memory.

[ssvss]

Do you know if Apple's M1 also does something similar to what is done by Fusion IO. I read something about it in Twitter, but didn't think to follow up with the twitter poster at that time.

[jng]

Thank you, note taken, that is very valuable information! OpenSSD is at least a good starting point to research and prototype, even if manufacturer help is needed later.