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by Saiprasad Parkar, Pratikkumar Shaha | Published February 25, 2013
The Subsystem Device Driver (SDD)
is a software solution to support the multipath configuration environments in supported storage devices. It resides in a host system with the native disk device driver and provides the following functions:
The following hardware components are needed:
The following software components are needed:
You can download the necessary package from the Subsystem Device Driver Path Control Module (SDDPCM) page.
Before you install SDDPCM, you must:
You need to perform the following steps to install the SDDPCM driver.
#installp -aXY devices.fcp.disk.ibm.mpio.rte
#installp -aXY devices.sddpcm.61.rte
#installp -aXY devices.sddpcm.126.96.36.199.2.bff
After this installation, you need to set a SDD path-selection policy algorithm that can help you to increase the performance of multipath-configured and supported storage devices and make path failures transparent to applications. The following path-selection policies are supported:
You need to choose the best suitable SDD path-selection policy to your environment and apply it using the following method.
Note: Before changing the algorithm, you need to change the disk reservation policy to no_reserve.
# chdev -l hdiskX -a reserve_policy=no_reserve
Examples of commands to set different SDD path-selection policy algorithm
#chdev ‑l hdiskX ‑a algorithm=load_balance_port
#chdev ‑l hdiskX ‑a algorithm=round_robin
You can check the disk policy using the pcmpath query device command.
pcmpath query device
You can also check the FCS adapter usages using the nmon tool. This tool helps to understand which FCS adapters are being used.
Important SDDPCM commands and their functions:
pcmpath query adapter:
pcmpath query version:
pcmpath query device:
pcmpath query essmap:
pcmpath set device algorithm:
pcmpath set device hc_mode:
pcmpath set device hc_interval:
pcmpath set device Mpath N online/offline:
pcmpath set adapter N online/offline:
pcmquerypr -vh /dev/hdisk30:
pcmquerypr -rh /dev/hdisk30:
pcmquerypr -ch /dev/hdisk30:
pcmquerypr -ph /dev/hdisk30:
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