Table of Contents
Advertisement
BIT
BYTE
7
6 5 4
3
2
I
0
------------;l;~~~:~I------I-----I~~~/~~~I;~;~~~!-;;~:-
-----------------------------------~--------------------
01
Number of Blocks (MSB)
02
Number of Blocks
03
Number of Blocks (LSB)
04
Logical Block Address (MSB)
05
Logical Block Address
06
Logical Block Address
07
Logical Block Address (LSB)
Figure 6-28.
Extent Descriptor Format
The size of the Extent List is defined
by the Extent List Length
parameter in the COB.
The ACB-5500 requires the length to be
either 8 or 0.
The Extent Descriptor defines an extent beginning
at the specified Logical Block Address (Bytes 04 through 07) for
the specified Number of Blocks (Bytes 01 through 03).
If the
Number of Blocks is zero, the extent
begins at the specified
Logical Block Address and continue through the last Logical Block
Address on the unit.
The Reservation Type field (Bits I through 0 of Byte 00) deter-
mines the type of reservation to be effected for each extent.
Four types of reservations are possible as follows:
Code
10
01
11
00
Reservation
~
Read Exclusive
Write Exclusive
Exclusive Access
Read Shared.
While Read Exclusive is active,
no other Initiator shall be
permitted READ access to the indicated extent.
This reservation
shall not inhibit WRITE accesses from any Initiator or conflict
with a Write Exclusive reservation;
however, Read Exclusive,
Exclusive Access, and Read Shared reservations which overlap this
extent shall conflict with this reservation.
500504-00
6-38
Advertisement
Table of Contents
