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Apparent issues with ZFS on RPi 5 (lemmy.world)

submitted 3 days ago* (last edited 3 days ago) by ramenshaman@lemmy.world to c/selfhosted@lemmy.world

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I tried to find a more applicable community to post this to but didn't find anything.

I recently set up a NAS/server on a Raspberry Pi 5 running Raspberry Pi OS (see my last post) and since then I've got everything installed into a 3D printed enclosure and I've got RAID set up (ZFS RAIDz1). Prior to setting up RAID, I could transfer files to/from the NAS at around 200MB/s, but now that RAID is seemingly working things are transferring at around 28-30 MB/s. I did a couple searches and found someone suggesting to disable sync ($ sudo zfs set sync=disabled zfspool). I tried that and it doesn't seem to have had any effect. Any suggestions are welcome but keep in mind that I barely know what I'm doing.

Edit: When I look at the SATA hat, the LEDs indicate that the drives are being written to for less than half a second and then there's a break of about 4 seconds where there's no writing going on.

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[–] Creat@discuss.tchncs.de 2 points 3 days ago* (last edited 3 days 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. By default on most distros, ARC size is capped to 50% of physical system memory. Keep in mind it is a cache: if something else needs needs the RAM, it will be released.

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.