Determines the maximum size of the ZFS Adjustable Replacement Cache (ARC). See also zfs_arc_min.
Unsigned Integer (64-bit)
Three-fourths of memory on systems with less than 4 Gbytes of memory
physmem minus 1 Gbyte on systems with greater than 4 Gbytes of memory
64 Mbytes to physmem
Yes, the range is validated.
If a future memory requirement is significantly large and well defined, you might consider reducing the value of this parameter to cap the ARC so that it does not compete with the memory requirement. For example, if you know that a future workload requires 20% of memory, it makes sense to cap the ARC such that it does not consume more than the remaining 80% of memory.
For information, see zfs_arc_max (Solaris 10 Releases).