Via river

Limit ZFS Memory Usage

It is good to use at most 50 percent (which is the default) of the system memory for ZFS ARC to prevent performance shortage of the host. Use your preferred editor to change the configuration in :

nano /etc/modprobe.d/zfs.conf 

options zfs zfs_arc_max=8589934592

8G = 8589934592
16G = 17179869184
32G = 34359738368