VERITAS Volume Manager

Legacy device special files on the /dev/dsk and /dev/rdsk directories:

These device files are only created for the first 32,768 paths on a system. Such device files can be discovered by VxVM DMP, and coexistence is supported. VxVM DMP works as a pass-through driver, and directs I/O and ioctl requests on one path without any load balancing. Native multi-pathing on HP-UX 11i v3 performs all multi-pathing and load balancing.

Device special files on the /dev/disk and /dev/rdisk directories:

One device file is created to represent each native multi-pathing metanode. These device files are created for all paths on a system, and more than 32,768 paths are supported. Such device files are not discovered by VxVM DMP and, coexistence is not supported. During device discovery, VxVM creates entries in the DMP database for the relationships between DMP nodes and the legacy device paths. Each DMP node represents a set of legacy paths. The legacy paths map internally to a native multi-pathing metanode that controls a set of physical paths. Native multi-pathing on HP-UX 11i v3 takes care of load balancing, failover and failback for the paths that it controls. The default I/O policy for VxVM DMP is set to single active for all types of enclosure. When VxVM DMP receives or sends I/O on a legacy path, native multi-pathing chooses the appropriate physical path. Unless all the underlying physical paths of the native multi-pathing metanode fail, any I/O that VxVM DMP performs on a legacy path succeeds.

VxVM DMP supports the A/P arrays that are supported by HP-UX native multi-pathing. No additional A/P arrays are supported. If an A/P array is used that is not supported by HP-UX native multi-pathing, any I/O or ioctl requests from VxVM DMP cause trespass.

A path-specific attribute that is shown by the DMP vxdmpadm getsubpaths command may not match the actual array attribute. This is because VxVM DMP cannot perform path-specific I/O or ioctl requests unless legacy multi-pathing is disabled. Instead VxVM DMP shows the path attributes that are returned by HP-UX native multi-pathing. For example, on an A/P array, all paths may be shown as PRIMARY or SECONDARY.

For A/A arrays, the vxdmpadm getsubpaths command shows all paths in the ENABLED (A) state until the last path is disabled. For arrays of type A/P, only one path is shown in the ENABLED (A) state.

VxVM DMP does not perform failover when a path to a LUN fails. VxVM DMP still shows the state of the path as active until HP-UX native multi-pathing fails an I/O or ioctl() request on that path.

The output from the vxdmpadm iostat command does not match the output from the native HP-UX iostat command.

Using the vxdmpadm disable and enable commands on a path or controller causes DMP to use another path for I/O, but HP-UX native multi-pathing may still be sending I/O to the disabled path or controller.

VERITAS Volume Manager 4.1 Release Notes

VERITAS Volume Manager 4.1 Administrator’s Guide