hdparm has a hard-coded timeout for the --security-erase and
--security-erase-enhanced commands of 2 hours.
However, this timeout value is not nearly long enough for current large hard
$ hdparm -I /dev/sdb | grep -E 'Model|device size|ERASE'
Model Number: WDC WD15EADS-00P8B0
device size with M = 1024*1024: 1430799 MBytes
device size with M = 1000*1000: 1500301 MBytes (1500 GB)
348min for SECURITY ERASE UNIT. 348min for ENHANCED SECURITY ERASE UNIT.
In other words, it will take just under 6 hours for the SECURITY ERASE command
to complete on this drive.