>> The hanging behavior is like a step function: the computer goes from being
>> fully responsive to completely unresponsive;
>
> That's very much unlike a normal "out of RAM" situation, OTOH.
> Normally what happens is that the OS starts to shuffle things around
> (throwing out cached data, moving other to swap, etc...) making the
> machine slower and slower.
>
> The step function sounds much more like a bug such as a deadlock.
Thank you for clearing up my misunderstanding of the observed behavior!
Indeed, Linux-Fan linked to the swap deadlock issue with ZFS.
> You could run a`memtester` process and tell it to test, say 6GB, so you
> the kernel only has 2GB left to play with and it will be forced to push
> stuff to swap, which you should then see in the output of `free`.
Thank you to you, Charles, and Tixy, for the suggestion to use `free`; I had
only previously used it to check RAM usage and did not know it's usefulness to
also check swap. As Tixy mentions, `free` does show zeros now that I have swap
disabled:
$ free
total used free shared buff/cache available
Mem: 8100708 4136324 2972808 197340 991576 3597312
Swap: 0 0 0
> You might want to try and set that same machine up with an ext4
> filesystem instead temporarily to see if you can reproduce the problem
> even without the use of ZFS (depending on how ZFS is used and your disk
> setup, it might be possible to do it easily, without having to
> reinstall (which could result in a sufficiently different system that
> it'd then be hard to convince oneself that the only difference is
> ZFS-vs-ext4)).
I actually was using ext4 for a few years on this machine before switching to
ZFS in June and it behaved well, right up to the point where it didn't - I have
had a few long power outages in my rural area, and running LUKS on LVM with
ext4 after 1 particular power outage made it irrecoverable with my abilities.
Which is why I switched to using encrypted ZFS. Though I in no way wish to
suggest encrypted ZFS is more reliable than LUKS on LVM with ext4; minus the
encryption, my colleagues have had fewer instances of disk corription with ZFS
and so I'm experimenting with it.
> Stefan
Pariksheet
