You can use the fsstat command to monitor file systems and report about file system operations. There are several options that report different kinds of activity. For example, you can display information by mount point or by file system type. In the following example, the fsstat command displays all of the ZFS file system operations from the time that the ZFS module was initially loaded:
$ fsstat zfs new name name attr attr lookup rddir read read write write file remov chng get set ops ops ops bytes ops bytes 268K 145K 93.6K 28.0M 71.1K 186M 2.74M 12.9M 56.2G 1.61M 9.46G zfs
See fsstat (1M) for other examples.