SCSI-2
The allocation length field specifies the maximum number of bytes
that an initiator has allocated for returned data. An allocation
length of zero indicates that no data shall be transferred. This
condition shall not be considered as an error. The target shall
terminate the DATA IN phase when allocation length bytes have been
transferred or when all available data have been transferred to the
initiator, whichever is less. The allocation length is used to limit
the maximum amount of data (e.g. sense data, mode data, log data,
diagnostic data, etc.) returned to an initiator.