IBM System Storage DS3500 Introduction And Implementation Manual page 109

Draft Document for Review March 28, 2011 12:24 pm
controller are transferred to the alternate controller, which is the configuration setting for
Microsoft Windows, IBM AIX, and Linux (when using the RDAC or SDD driver and
non-failover Fibre Channel HBA driver) systems.
When ADT is disabled, the I/O data path is still protected as long as you use a multi-path
driver. After the I/O data path problem is corrected, the preferred controller does not
automatically reestablish ownership of the logical drive. You must open a storage
management window, select Redistribute Logical Drives from the Advanced menu, and
perform the Redistribute Logical Drives task.
Figure 3-27 shows the ADT-disabled failover mode phases.
Application
1
Host / Server
Port 0 receive an error.
connection is no longer
valid, error is passed on
to the failover driver
- 020 failed
- 130 alternate
Application
3
Host / Server
The failover driver can
now use the alternate
path for any retried or
new I/Os
- 020 failed
- 130 current
Figure 3-27 ADT-disabled mode path failover
Note: In ADT-disabled mode, you are required to issue a redistribution command
manually to get the LUNs balanced across the controllers.
A
[2]
0
X
1
B
[3]
Application
X
Host / Server
A
[2]
0
X
1
B
[3]
Application
X
Host / Server
Chapter 3. IBM System Storage DS3500 Storage System planning tasks
7914DS3KPlanning_090710.fm
Application is using LUN 0
0 1 2 3
Failover driver hides the
two physical paths to LUN
- 020 current (colored)
- 130 alternate (white)
1 2 3
0
A
0
[2]
0
1
B
[3]
0
Failover driver determine
usage of alternate path
0 1 2 3
to continue I/O. Send a
Mode Select SCSI command
to the storage. Volume
ownership changes as a
result of SCSI mode
1 3
0 2
select command.
- 020 failed
A
0
[2]
0
1
B
[3]
0
1 2 3
2
1 2 3
1 3
2
4
1 3
2
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