There can be many reasons for PowerPath for Windows to report a path dead situation.
1.powermt.custom or powermt.custom.xml file issue.
Depending on the version of PowerPath the file will be created in either of the following folders.
The file can be created in one of 2 ways. Either issuing the command “powermt save” or pressing the Yes button on exiting the PowerPath Administration GUI.
The reason why this file can create dead paths is down to how Microsoft Windows assigns HBA controller numbers at boot time.
There is no guarantee that the HBA controller numbers will be maintained across reboots unless static binding is in use.
The powermt.custom(.xml) file stores the paths seen by PowerPath at the time of the save (in the format of CTD) amongst a lot of pathing information.
When Windows is rebooted the OS will scan the various buses for HBAs and assign them controller numbers (if static binding is not in operation).
PowerPath will pick these controller numbers up and create PowerPath devices using the paths it finds on these HBAs.
It will also load the details of the powermt.custom(.xml) file and add any paths for these devices that have not already been found.
If the HBA controller numbers before and after the reboot are not the same this will result in ‘duplicate paths’ using different HBA instances connecting to the Array ports. The paths as stored in the powermt.custom(.xml) file will appear as dead.
2.If on the rare occasion an HBA does in fact go bad then this may necessitate replacing the HBA.
3.Either MPIO failing to claim the device or MPIO claiming the device and not passing to PowerPath.
4.Unsupported HBA configurations. If the HBA BIOS/Firmware/Driver combination is mismatched by too great a time (old firmware with new drivers or vice versa).
5.Devices appearing in device manager with a ‘Yellow Exlamation mark”.
6.Third Party Devices or EMC VPlex in use.
7.Fabric rebuilds due to components on the fabric being added or removed if the rebuild takes too long can result in path dead.
8.Zoning has been changed whether accidentally or on purpose.
9.If a Symmetrix environment and masking and/or mapping has been changed.
10.If a CLARiiON/VNX environment and either the logical paths have been changed or the device(s) have been removed from the storage group.
11.HBAs not registered on the CLARIiON/VNX.
12.Physical issues with fabric and/or Array.