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I would like to ask about MLC NAND support in UBIFS as of 2021.

I was recently bringing up a device with IMX6ULL and raw MLC NAND flash. I have built Linux 5.4 kernel, u-boot and rootfs (using buildroot), flashed them to my device with MLC NAND flash, and learned from dmesg error that MLC is unsupported by ubifs. Support removed in this commit: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b5094b7f135be

Then I followed the story from Richard and Boris and watched the talk where they explain the issues with MLC, and propose an alternative: https://www.youtube.com/watch?v=9j2pOIiJqYw&ab_channel=TheLinuxFoundation Alternative available since Linux 5.8: https://www.phoronix.com/scan.php?page=news_item&px=Linux-5.8-NAND-MLC-SLC-Emulate

I have seen the question Linux: Alternative to UBIFS on MLC NAND, however there was some work in kernel / ubifs since 2018, e.g. the SLC emulate mode.

My question:

  • Is NAND MLC (+ubifs) reliable to use with SLC emulate mode introduced in kernel 5.8? Or should I rather switch to eMMC for this design? SLC NAND is too costly at my required flash size. I'm using IMX6ULL processor, and I have a small backup battery on the board (so power cuts may be not a big issue).
Filip Kubicz
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  • One note to kernel 5.8, my Mint shows it as deprecated. – Vlastimil Burián Sep 26 '21 at 11:34
  • I can use kernel 5.10 LTS on my IMX6ULL. Does not really matter, as long as it has the features needed (5.8+). I create my system using buildroot. – Filip Kubicz Sep 26 '21 at 12:30
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    I can't comment on the reliability of that combination. I as well as most of the industry prefer eMMC if your design is more in the range of tenthousands than of millions of pieces, with two considerations: 1) The whole logic of wear leveling and defect management is encapsulated and as close as possible to the flash level. 2) You can easily replace your eMMC without any adoption of geometry or timings or whatever in the BSP, which is an advantage that hardly can be overestimated in these times of supply shortage all around. – Philippos Sep 26 '21 at 14:04

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