TAH_Changing block size on SCSI hard disk

Changing the block size on SCSI hard disks.

SCSI disk drives arrive from the factory already low-level formatted to a specific block length indicated by the model. A typical and popular length would be 512 bytes. Some operating systems and specialist systems demand a different block length such as 256 bytes or the more efficient 1024 bytes. If the block length needs to be changed, the IDD must be reformatted according to the following procedure.

This procedure should only be performed by personnel who are fully conversant with low-level SCSI device commands.

This procedure only applies to disk drives where stated in the specifications that the block size may be changed.

Connect the IDD to the system and turn on the power
Issue a MODE SELECT command specifying the new data block length as shown below.
Issue a FORMAT UNIT command. The disk medium is reformatted with the specified block length, and the alternate block assignment for the medium defects is performed according to the primary defect list

Notes

After issuing the MODE SELECT in step 2, move straight on to step 3. Issuing say a READ CAPACITY command will generate an error if issued when the medium is in an unknown state.

Under no circimstances must the SCSI low-level format be interrupted once started. A failing power supply at this point can cause irrepairable damage to the drive.

The block length used above is for example only. Block lengths on some Fujitsu drives may be set from 180 bytes to 4160 bytes in even two byte increments. Refer to the drive specifications for more details.