Dynamic Multipathing with VXDMP

DMP (Dynamic Multipathing):-

This is a feature available in Vxvm to provide reliability, redundancy and availability of data. DMP is automatically configured when we install veritas. With DMP we can connect multiple paths to an multiported array.

Multiported disk arrays can be connected to the host system through multiple paths. Till veritas 3.2 we can connect a max of 32 paths to a single server. From 4.x onwards the count is unlimited.

When multi paths are connected DMP uses a mechanism that is specific to each supported disk array.

Veritas will automatically identify the available paths to a single physical storage with the help of world wide unique identifier and perform IO operation to the physical device without any interruption with the help of available paths.

DMP supports following types of array types

1. Active/Active:  Allows server paths to be used concurrently for IO  operations. In this type of array DMP provides greater through put by balancing IO uniformally.  Across multiple paths. In this case if one path fails, IO operations are automatically moved to the next available paths.
2. Active/Passive: This type allows access to disk or LUN’s via primary path which is active, if primary path fails it goes secondary path.

To administer dynamic multipathing we use the following commands:

# vxdmpadm: Lists the available paths.

Displays information about HBA controllers on the host. Displays info about enclosure’s. Gaters IO statistics for DMP mode.

Set the IO policy.

Set the partition size or rename the enclosure.

# vxdisk path (To the the list of controllers & enclosures)

# vxdmpadm list ctrl all | more (To set the sub paths in a enclosure)

# vxdmpadm getsubpaths ctrl=c1 (To get the info about enclosure)

# vxdmpadm listenclosure sena0

# fcinfo hba-port

# vxdmpadm getdumpnode enclosure=sena0

To gather the IO stats of DMP

# vsdmadm iostat start

# vsdmpadm iostat show all

# vxdmpadm iostat reset

# vxdmadm iostat stop

To display the IO policy

# vxdmpadm getattr enclosure SENA0 iopolicy

# vxdmadm setattr enclosure SENA0 iopolicy=round-robin

To display the partition size

# vxdmpadm getattr enclosure SENA0 partionsize

To rename enclosure

# vxdmpadm setattr enclosure SENA0 name=SENA0

# vxdiskadm