134 IBM Midrange System Storage Hardware Guide
When you create a logical drive, you assign one of the two active controllers to own the logical
drive (called
preferred controller ownership, as described in 4.1.2, “Logical drives and
controller ownership” on page 114) and to control the I/O between the logical drive and the
application host along the I/O path. The preferred controller normally receives the I/O
requests from the logical drive. If a problem along the data path (such as a component failure)
causes an I/O to fail, the multipath driver issues the I/O to the alternate controller.
A multipath device driver is not required when the host operating system has its own
mechanism to handle multiple I/O paths, but if not, you have to install the supplied multipath
device driver, even if your server does not has multiple paths.
Table 4-5 shows the DS5000 storage subsystem interoperability matrix of multipathing
drivers.
Table 4-5 DS5000 storage subsystem interoperability matrix of multipathing drivers
Load Balancing Policy
When you have multiple paths to the DS5000 storage subsystem, the driver can select
between different options about how to manage the traffic between the host and storage. The
options available for the different operative systems are shown in Table 4-6.
Table 4-6 Load Balancing Policies per OS
Windows
2003/2008
RHEL SLES AIX 5L
V5.3
AIX
V6.1
HP-UX
11.23
HP-UX
11.31
DS5000 RDAC X X
Win MPIO X
AIX MPIO X
a
a. Included in the operating system
X
a
AIX SDDPCM X X
LVM (HP-UX) X X
SDD for HP-UX X
Operating system Multipath driver Load Balancing Policy
AIX MPIO Round robin
Selectable path priority
Red Hat Enterprise Linux 4 Update 7 MPP Round robin
Least queue depth
Solaris MPxIO Round robin
SUSE Linux Enterprise 9 Service Pack 4 MPP Round robin
Least queue depth
Windows MPIO Round robin
Least queue depth
Least path weight
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