4 ms·

I'm afraid I don't get this at all. Use of data should define the data... > The reason why ext4 and xfs both use nanosecond resolution is because in the kernel

I'm afraid I don't get this at all. Use of data should define the data... > The reason why ext4 and xfs both use nanosecond resolution is because in the kernel the high precision time keeping structure is the timespec structure ...so resolution here is defined by what's provided, not what's (decided to be) useful. Is ns resolution useful is the important question. > Why not use a finer granularity? Because space in the on-disk inode structure is precious That's not a good reason AFAICS. What would it gain your users if you did? 1 ns = ~4 machine cycles. Timestamping to that res, well, what's the value to any application? I'm missing something.

emteycz 6y ago
You can sometimes see timestamps from other machines too, they can also be parallel
- throwaway_pdp09 6y ago
  I'm being dense, I don't understand what you're saying. Could you give a bit more detail please?
  - emteycz 6y ago
    What my machine can or can not do is irrelevant, I might connect a drive from a machine where machine cycles were faster or parallel. So it's entirely possible to see timestamps less than X nanoseconds apart even if my machine can't do more than one cycle each X nanoseconds.
    - throwaway_pdp09 6y ago
      How would that make any possible difference to you? Bear in mind 1ns = the time a ray of light would travel 30cm in a vacuum.
      - emteycz 6y ago
        I imagine it could make a difference in court in some cases.
        throwaway_pdp09 6y ago
        With respect, no way. FIPS mandates a timestamp resolution of 10 microseconds. 10,100 times smaller that is literally meaningless.
        emteycz 6y ago
        Thanks for correcting me on that! I still think it could be useful to people, though. Do you think it's that wasteful? The machines of today are powerful and have plenty of disk space.
        throwaway_pdp09 6y ago
        That's a good question and it's philosophical. Perhaps it may/may not be wasteful, but it's meaningless therefore useless. If they said "we'll store it to the nanosecond because the kernel does" I'm OK with that if - very big if - they make it clear that it does not have accuracy in the last few digits. They need to say clearly what max accuracy you can expect. To then talk about storing it with finer accuracy after that... just what? Also be careful about thinking machines having big everything. Caches aren't huge, storing an extra byte if a billion places can add up at scale. Nothing comes free, don't scrimp where you don't have to but neither assume anything's free. HTH. IMO only.

emteycz 6y ago

You can sometimes see timestamps from other machines too, they can also be parallel

throwaway_pdp09 6y ago
I'm being dense, I don't understand what you're saying. Could you give a bit more detail please?
- emteycz 6y ago
  What my machine can or can not do is irrelevant, I might connect a drive from a machine where machine cycles were faster or parallel. So it's entirely possible to see timestamps less than X nanoseconds apart even if my machine can't do more than one cycle each X nanoseconds.
  - throwaway_pdp09 6y ago
    How would that make any possible difference to you? Bear in mind 1ns = the time a ray of light would travel 30cm in a vacuum.
    - emteycz 6y ago
      I imagine it could make a difference in court in some cases.
      - throwaway_pdp09 6y ago
        With respect, no way. FIPS mandates a timestamp resolution of 10 microseconds. 10,100 times smaller that is literally meaningless.
        emteycz 6y ago
        Thanks for correcting me on that! I still think it could be useful to people, though. Do you think it's that wasteful? The machines of today are powerful and have plenty of disk space.
        throwaway_pdp09 6y ago
        That's a good question and it's philosophical. Perhaps it may/may not be wasteful, but it's meaningless therefore useless. If they said "we'll store it to the nanosecond because the kernel does" I'm OK with that if - very big if - they make it clear that it does not have accuracy in the last few digits. They need to say clearly what max accuracy you can expect. To then talk about storing it with finer accuracy after that... just what? Also be careful about thinking machines having big everything. Caches aren't huge, storing an extra byte if a billion places can add up at scale. Nothing comes free, don't scrimp where you don't have to but neither assume anything's free. HTH. IMO only.