5.8FORMAT UNIT Command (04h)
The FORMAT UNIT command formats the disk's storage media into initiator- addressable logical blocks according to
This command repairs damage left by previous WRITE LONG commands. The WRITE LONG command allows the initiator to deliberately corrupt a sector's ECC or EDC.
The FORMAT UNIT command updates the defective sector list, referred to as the Grown Defect List, that is maintained by the drive. As described below, the drive gives the initiator considerable control over this list. If certification is enabled, all initiator- addressable logical blocks are verified, and bad sectors are reassigned and added to the Grown Defect List.
Note: During FORMAT UNIT command processing, the drive ignores the Read/Write AWRE and ARRE bits (from Error Recovery Mode page) and does
The drive is physically formatted when it leaves the manufacturing facility. Therefore, it is not necessary to reformat the drive before using it. If the logical sector size of the drive is changed using the Block Descriptor of the MODE SELECT Command, it is recommended (but not necessary) to reformat the drive.
The Immed bit that can be included in the FORMAT UNIT command parameter list allows the initiator to control whether the drive returns completion status either after fetching and validating the Command Descriptor Block and parameter list or after the FORMAT UNIT command completes. The FORMAT UNIT command parameters are described in Table
The time required for the FORMAT UNIT command to format the disk primarily depends on the capacity of the drive. The number of defects detected and the number of defects already in the Primary and Grown Defect Lists also influence the time required to format the drive. If the Disable Certification bit is set to 1, formatting time is reduced.
Defective sectors on the drive are managed through two lists: the Primary Defect List and the Grown Defect List. The Primary Defect List is created when the drive is manufactured and is the drive's initial defect list. The Primary Defect List is not affected by the FORMAT UNIT command. Sectors listed in it are revectored by the drive. The Grown Defect List contains a list of the sectors that have gone bad since the drive's primary list was generated.
Defects are communicated in a data structure referred to as a Defect Descriptor. The SCSI specification defines several Defect Descriptor formats. The FORMAT UNIT command recognizes defect descriptors in Block format, Bytes From Index format, and Physical Sector format. (There is one exception: a value of FFFFFFFFh in either the defect Bytes From Index field or the Defective Sector Number fields is ignored).
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