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Comment by nolist_policy

2 years ago

I still don't think this is the problem, the drive can just slow down accepting writes until it has reclaimed enough space.

The bigger problem is manufacturers chasing the performance. Generally you get the feeling they just hit their firmware with a hammer so it barely doesn't break NTFS.

See also the drama around btrfs' "unreliability", which is all traced back to drives with broken firmware. I fully expect bcachefs will get exactly the same problems.

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nolist_policy

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kmxdm  2 years ago

Yeah, but then you have a write amplification problem. Padding is write amplification from the start, and then GC is invoked many more times than it otherwise would be. There is a fundamental problem with (truly) flushing an IO that is smaller than the media write unit. It will cause problems if "abused." The SSD either needs to take on the cost of mitigation (e.g. caps) or it needs some way to provide hints to the host that don't exist today.

  • nijave  2 years ago

    I'm curious what the real cost of power protection is for the manufacturer. Adding caps or a bit of backup power seems like it _should_ be a fairly cheap compromise to maintain performance without lying about persistence

    • kmxdm  2 years ago

      M.2/2280 makes it hard. Can't use cheaper aluminum can capacitors due to their size/height. The low profile (tantalum?) capacitors are expensive and take up a lot of PCB area, forcing a two sided PCB design on 2280 (the 110mm version would be better here). M.2 only provides 5V. On other form factors you get 12V and can get more charge stored for the same capacitance (q=CV) without needing a DC-DC converter.

    • justsomehnguy  2 years ago

      define 'cheap'?

      You already have the device shipped to you under $40 with packaging, shipping from China, to the distributor, to you; with a profit at the every step.

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