Comment on Apparent issues with ZFS on RPi 5
Creat@discuss.tchncs.de 3 weeks ago
What size is the ARC set to? I’ve seen cases where it was fully disabled, which seemed to murder performance and is probably even worse when in such a CPU limited platform.
ramenshaman@lemmy.world 3 weeks ago
I don’t know what ARC is and my searches so far haven’t helped.
3dcadmin@lemmy.relayeasy.com 3 weeks ago
this is the limits of a slow interface and 5 drives. See my other reply to enable faster pci speeds. because of how zfs works 5 drives is slower than 3, takes more cache and write speeds especially will be slower, quite a lot slower. with 5 drives and 16gb you can easily have a zfs cache of 12 gigs to help it along, i guess this is why you are getting large gaps between writes. as someone else said a pi doesn’t do well in this case but I reckon you can improve it. however as also said it is never going to be a speedy solution. secure and safe for data but not fast
Lemmchen@feddit.org 3 weeks ago
Do you have the 8GB version of the Pi 5? You shouldn’t set the ARC to 8GB then. Usually it about half of the available system RAM. I’d probably set it lower if there’s only 8GB available in total.
ramenshaman@lemmy.world 3 weeks ago
16GB of RAM. I figured it might be overkill but I went all-in anyways.
Creat@discuss.tchncs.de 3 weeks ago
ARC is the in-memory cache used by ZFS. If it’s completely off the effect can be dramatic. Under no circumstances should a larger cache cause anything to get slower, ever. Even the raspi didn’t have memory that is that slow that this is a reasonable outcome.
As a concrete example: I was recently working on a server where a maintenance task that should take like 12hrs or so at the worst somehow took 2 weeks (!) and still wasn’t finished. That was ARC being disabled.