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About the SCSI Format Unit Command
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(from the Seagate SCSI Commands Reference Manual, 100293068 Rev. H July 2014)
http://www.seagate.com/files/staticfiles/support/docs/manual/Interface%20manuals/100293068h.pdf

The FORMAT UNIT command requests that the device server format the medium into
application client accessible logical blocks as specified in the number of
blocks and block length values received in the last mode parameter block
descriptor in a MODE SELECT command. In addition, the device server may certify
the medium and create control structures for the management of the medium and
defects. The degree that the medium is altered by this command is
vendor-specific.

If a device server receives a FORMAT UNIT command before receiving a MODE
SELECT command with a mode parameter block descriptor the device server shall
use the number of blocks and block length at which the logical unit is
currently formatted (i.e., no change is made to the number of blocks and the
block length of the logical unit during the format operation).

The simplest form of the FORMAT UNIT command (i.e., a FORMAT UNIT command with
no parameter data) accomplishes medium formatting with little application
client control over defect management. The device server implementation
determines the degree of defect management that is to be performed. Additional
forms of this command increase the application client's control over defect
management.

The application client may specify:
  a) defect list(s) to be used;
  b) defect locations;
  c) that logical unit certification be enabled; and
  d) exception handling in the event that defect lists are not accessible.

While performing a format operation, the device server shall respond to
commands attempting to enter into the task set except INQUIRY commands, REPORT
LUNS commands, and REQUEST SENSE commands with CHECK CONDITION status with the
sense key set to NOT READY and the additional sense code set to LOGICAL UNIT
NOT READY, FORMAT IN PROGRESS. Handling of commands already in the task set is
vendor-specific. If the device server receives an INQUIRY command, a REPORT
LUNS commands, or a REQUEST SENSE command, then the device server shall process
the command. The device server shall return data for an INQUIRY command based
on the condition of the SCSI target device before beginning the FORMAT UNIT
command (i.e., INQUIRY data shall not change until after successful completion
of a format operation). The processing of commands in the task set when a
FORMAT UNIT command is received is vendor specific.

