7914DS3KPlanning_090710.fm Draft Document for Review March 28, 2011 12:24 pm
86 IBM System Storage DS3500: Introduction and Implementation Guide
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, which is the normal configuration setting for Novell
NetWare, Linux (when using FC HBA failover driver instead of RDAC), and Hewlett
Packard 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.
Phases of failover
Figure 3-28 shows the phases of failover in an ADT-enabled case.
Figure 3-28 ADT-enabled mode path failover
3.7 Operating system restrictions
In your planning, you must also consider the restrictions of your operating system that might
apply. We have covered the maximum file system size ordered by the operating system and
their commonly used file systems, the maximum number of LUNs that can be assigned to one
host, and the maximum logical volume size supported by various operating systems.
Note: In ADT mode, RDAC automatically redistributes the LUNs to their preferred path
after the failed path is again operational.
Host / Server
1
0
1
2
3
1
2
3
A
[2]
B
[3]
Failover Driver
X
Application
0
0
Host / Server
1
0
1
2
3
1
2
3
A
[2]
B
[3]
Failover Driver
X
Application
0
0
Phase1-2 see Figure 3-27
The LUN 0 volume
transfers to controller B
which currently has I/O
activity for that volume.
- 020 failed
- 130 current
The failover driver will
choose to use the
alternate path for any
retried or new I/Os.
- 020 failed
- 130 current
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