20130605: Added ZFS TRIM support which is enabled by default. To disable ZFS TRIM support set vfs.zfs.trim.enabled=0 in loader.conf. Creating new ZFS pools and adding new devices to existing pools first performs a full device level TRIM which can take a significant amount of time. The sysctl vfs.zfs.vdev.trim_on_init can be set to 0 to disable this behaviour. ZFS TRIM requires the underlying device support BIO_DELETE which is currently provided by methods such as ATA TRIM and SCSI UNMAP via CAM, which are typically supported by SSD's. Stats for ZFS TRIM can be monitored by looking at the sysctl's under kstat.zfs.misc.zio_trim.