14.2 Enabling Multipath

Multipath I/O is disabled by default. If your devices do not have multiple paths, then multipath support should be disabled; you do not need it.

Before enabling multipath support, you need to determine if the a device’s HAM driver handles multiple paths to devices. Check to see if the HAM driver presents only one path to a given device even if there are multiple adapters and multiple ports connected to the same storage device.

To check the HAM driver, you can scan devices (SCAN ALL), then list them (LIST DEVICES). If you can see a given LUN multiple times, then you need to enable multipath support. If a device should have multiple paths and does not, either you have a hardware configuration problem or a driver problem, and you need to resolve the issue before you enable multipath support.

In order to enable multipath support, use the SET parameter under Disk > Multi-Path Support, or issue the following command at the NetWare server console:

set multi-path support = on

After enabling the parameter, you need to scan for new devices to allow Media Manager to recognize the new paths to the multipathed devices. For some storage arrays, a reboot might be required.

For persistence across reboots, you can add the following line near the top of the startup.ncf file and before any lines that load drivers:

set multi-path support = on

The scan for new devices occurs automatically on start-up.

If the HAM adapter is handling multipath for the devices, but you want NetWare MPIO to handle failover between paths, you need to disable the HAM driver’s multipath handling. Make sure the SAN manager is not managing the HBA devices, then add the /ALLPATHS and /PORTNAMES HBA load options (if appropriate for your configuration) to the HAM driver load lines in order to expose all device paths and ports to NetWare:

The /ALLPATHS option disables the HAM adapter’s path failover and reports to NetWare all devices on all adapter paths. All adapters report the same devices, which allows upper layer modules to fail over across a NetWare server’s multiple adapters.

The /PORTNAMES option tracks devices internally by port name rather than node name. It disables the HAM adapter’s storage port failover and reports all storage ports for each device on the reporting adapters. This is required when storage LUNs do not have a one-to-one correspondence across port names. This allows upper layer modules to fail over across a subsystem’s multiple ports.

For example:


Depending on your hardware configuration, specify one or both options if you want MPIO to handle paths to multiple adapters, multiple ports, or both multiple adapters and multiple ports.

The AEN (Asynchronous Event Notification) parameter for scsihd.cdm is also advisable if you are using Fibre Channel. When AEN is enabled, the HAMs that can, such as Fibre Channel, report the loss of a hard disk drive or the discovery of a new one even without active IO. The default value for AEN is off.

If scsihd.cdm is already loaded without the /AEN option, you can enter the following at the NetWare server console:

load scsihd.cdm /aen


load scsihd.cdm /aen

AEN functionality is seamlessly added to the driver without the driver re-loading or re-initializing.