You can use the sg_sanitize command to remove or scrub all the data from a disk. To invoke the sg_sanitize command, you must first install the pkg:/system/storage/sg3_utils package. The purpose of the sanitize operation is to alter the information in the cache and on the medium of a logical unit (for example, a disk) so that the recovery of the data is not possible. You can also scrub solid state drives (SSDs) using the sg_sanitize command.
Once the sg_sanitize command is started on a disk, then the data in that disk is no longer available. Even if the disk is power cycled, the sanitize operation will continue after power is re-instated until the operation is complete. For more information, see the sg_sanitize(1m) man page.