The design of littlefs: A fail-safe filesystem designed for microcontrollers • Hacker News Board

Re: The design of littlefs: A fail-safe filesystem designed for microcontrollers

#71

Post by ClumsyPilot » Sun, Sep 01, 2019, 4:34 PM UTC

benlwalker wrote: post #46

kabdib wrote: post #39

Earlier quoted context omitted.

No SSDs here, this is raw flash. This is the wear leveling layer.

I assumed so, but then why all the comparisons to file systems that are designed to run on top of a flash translation layer? I would have expected something in big bold letters at the top saying this is designed to run without an FTL, whereas the other filesystems rely on one to wear level. For example, this is right at the top: "Writing to flash is destructive. If a filesystem repeatedly writes to the same block, ev…

The domain comes with it's own shenanigans, and it's impractical to list all of them. When working with microcontrollers no-one should expect to have FTL.

Re: The design of littlefs: A fail-safe filesystem designed for microcontrollers

#72

Post by IA21 » Sun, Sep 01, 2019, 5:33 PM UTC

devwastaken wrote: post #53

_urga wrote: post #18

> Logging filesystem are beautifully elegant. With a checksum, we can easily detect power-loss and fall back to the previous state by ignoring failed appends. An edge case when designing a log-structured file system is that a corrupt checksum in a log entry could actually mean one of three things: power loss while writing the last transaction, a misdirected write or bitrot, or a misdirected read. If you simply read t…

Isn't that essentially sqlite?

I don't think sqlite would fit inside the microcontrollers this post is about.

Re: The design of littlefs: A fail-safe filesystem designed for microcontrollers

#73

Post by ianhowson » Mon, Sep 02, 2019, 1:15 AM UTC

ClumsyPilot wrote: post #70

nine_k wrote: post #41

Earlier quoted context omitted.

A compact and reliable 470 uF capacitor could cost comparable to to a low-end uC.

I mean, you get what you pay for. If your are cost-optimising that hard, you probably aren't controlling something with critical data.

If you aren't cost-optimizing that hard, you aren't shipping meaningful volumes yet. 470uF isn't cheap at 10k+ units.

My last project couldn't use a giant cap because of size, not cost constraints.

Re: The design of littlefs: A fail-safe filesystem designed for microcontrollers

#74

Post by varjag » Tue, Sep 03, 2019, 10:20 PM UTC

kabdib wrote: post #47

varjag wrote: post #45

Earlier quoted context omitted.

My understanding was if the function is interrupted on discharge, you fail the test. At least that's how our equipment was tested by an independent lab.

Might be different depending on the market. For us it was "we can reset, but we have to recover within a few seconds". I never questioned the wisdom of our hardware cert engineers. (My experience at three different companies spread over 35 years was, if you were a software engineer helping the hardware types with ESD or RFI testing in the lab, you were definitely going to get zapped at some point. That made you part…

As it was put to me, if a discharge leaks through, there's really good chance that another, or 3rd, or 5th would be fatal: the device is not adequately protected. But probably that's not a big deal in some applications.