Date:  Feb 16, 1993                      X3T9.2/93-032 rev 0


To:  X3T9.2 Committee (SCSI)

From:  George Penokie (IBM)

Subject:  Number of Blocks Field Size Limitation

The Number of Blocks field in the Mode Parameter Block
Descriptor (section 7.7.7, Table 93, SCSI-2 10h) is 3 bytes
in length.  This length only allows 16,777,215 blocks (8.59
GBytes for 512 byte blocks).

This size does not match the Read Capacity Command, which has
a Logical Block Address of 4 Bytes.  This length allows
4,294,967,295 blocks (2,199 GBytes for 512 byte blocks).

The 3 byte number of blocks field is not large enough to
handle RAID devices larger than 8.59 GBytes.

I propose that if FFFFFFh is in the Number of Blocks field it
shall be interpreted as the number of blocks is greater than
FFFFFEh.  If FFFFFFh is returned in the Number of Blocks
field the Read Capacity Command may be used to determine the
actual number of blocks for the device.

This change is proposed for SCSI-3 only.