TrueNAS SCALE 24.04.0 still have memory never be used

Hello guys. I have 512GB of memory in total. However, after upgrading to Dragonfish, which said it would use all the memory as ARC, there are still 30GB of memory that have never been used.

For 512GB in total, 30GB may be a small part. But 30GB of memory is still a giant one.

Note: I have disabled the zfs_arc_max modification command and enabled TrueNAS to manage the ARC size. Moreover, there are no virtual machines or K3S apps on my TrueNAS SCALE.

I can’t find it right now, but I think they put in a 1% buffer for k3s to keep it from crashing. Probably too much for a system with more memory like yours. They basically need 1GB of RAM free at all times.

It’s the same memory allocation calculation as on CORE now, which is the default in ZFS for safety reasons.

You can adjust it upwards if you want to get more aggressive in usage.


Trust your visual cortex when it tells you “hey, the free bit of the pie chart is small”. Sure, it’s 29 GB, but you can’t fill everything up to the top, otherwise things start to break left and right. That’s not a ZFS or Linux thing, it’s a “that’s how our model of computing works” kind of thing.