https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/htm...
Auszug:
|sg3_utils| component, BZ#1186462 Due to the conversion of the iprutils package to use |systemd| instead of legacy init scripts, the |sg| driver is no longer loaded during system boot. Consequently, if the |sg| driver is not loaded, the |/dev/sg*| devices will not be present. To work around this issue, manually issue |modprobe sg| or add it to an init script. Once the |sg| driver is loaded, the |/dev/sg*| devices will be present and the |sg| driver may be used to access SCSI devices.