How to prevent data loss when using blkdiscard on NetBSD

On Linux, this command fstrim -av I will remove all unused blocks (particularly interesting on VM disks and necessary on SSD to preserve/get a longer duration). NetBSD has a similar command called blkdiscard This command wipes the entire disk, so it becomes unusable (correct me if I am wrong) blkdiscard -v /dev/rwd... I see there is a flag which starts to discard after some bytes (or MB) blkdiscard -v -f 256m -m 128m /dev/rwd0c Suppose my partition uses 6GB of data, to make a safe discard (my data still remains), is this the correct command? blkdiscard -v -f 6000m -m 128m /dev/rwd0c