IBM System Storage DS4000, Hardware Manual

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IBM Midrange System Storage Hardware Guide
Figure 4-10 shows the ADT-disabled failover mode phases.
Figure 4-10 ADT-disabled mode path failover
򐂰 ADT-enabled failover
The multi-path driver starts using the alternate path by sending the I/O down the path it
chooses and lets the ADT react. This is the normal configuration setting for Novell
NetWare, Linux (when using the FC HBA failover driver instead of RDAC), and HP-UX
systems. After the I/O data path problem is corrected, the preferred controller
automatically reestablishes ownership of the logical drive as soon as the multipath driver
detects that the path is normal again.
Note: In ADT-disabled mode, you are required to issue a redistribution command
manually to balance the LUNs across the controllers.
Host / Server
1
0 1 2 3
1 2 3
A
[2]
B
[3]
X
Application
0
0
Host / Server
1
0 1 2 3
1 2 3
A
[2]
B
[3]
X
Application
0
0
Application is using LUN 0.
Failover driver hides the
two physical paths to LUN.
- 020 current (green)
- 130 alternate (white)
Port 0 receives an error.
Connection is no longer
valid, error is passed on
to the failover driver.
- 020 failed
- 130 alternate
1
2
Fail
ov
er
D
riv
er
F
a
ilo
ve
r D
riv
er
Failover driver determines
usage of alternate path to
continue I/O. Send a Mode
Select SCSI command to the
storage. Volume ownership
changes as a result of SCSI
mode select command.
- 020 failed
- 130 pending transfer
Host / Server
1
0
1
2
3
1
2
3
A
[2]
B
[3]
X
Application
0
0
Host / Server
1
0
1
2
3
1
2
3
A
[2]
B
[3]
X
Application
0
0
The failover driver can
now use the alternate
path for any retired or
new I/Os.
- 020 failed
- 130 current
3
4
Failov
er
Dri
ver
F
ailo
ve
r Dr
iv
er