How to use mkntfs, I get "not a block device"

[Thomas Mueller]

In running 
mkntfs -F /dev/gpt/SeaExp1-03

I got (do I need to be concerned?)

root at amelia:/usr/ports # mkntfs -F /dev/gpt/SeaExp1-03
/dev/gpt/SeaExp1-03 is not a block device.
mkntfs forced anyway.
The partition start sector was not specified for /dev/gpt/SeaExp1-03 and it could not be obtained automatically.  It has been set to 0.
The number of sectors per track was not specified for /dev/gpt/SeaExp1-03 and it could not be obtained automatically.  It has been set to 0.
The number of heads was not specified for /dev/gpt/SeaExp1-03 and it could not be obtained automatically.  It has been set to 0.
Cluster size has been automatically set to 4096 bytes.
To boot from a device, Windows needs the 'partition start sector', the 'sectors per track' and the 'number of heads' to be set.
Windows will not be able to boot from this device.
Initializing device with zeroes:   0% 
100% - Done.
Creating NTFS volume structures.
mkntfs completed successfully. Have a nice day.
root at amelia:/usr/ports # 


It took many hours, partition size was 500 GB, I let it run while I was in bed.


Tom