Multi-pathing

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From multi-pathing is when there a server is possible via several bus host adapter the same disk subsystem to achieve. This technology is particularly widespread in clustered environments and provides the necessary redundancy.

Operating modes

Active passive

If an active path fails, for example due to hardware damage, the data transfer can continue via the connections that are still available ( failover ) without affecting the programs running on the system.

Active / active

The data transfer between the two systems can be distributed over all existing data paths ( load distribution ). By using several host bus adapters in the disk subsystems and the servers, the possible overall transmission speed can be increased. Here, too, in the event of an error, the connections that are still present take over the ongoing data transfer if a path fails.

Implementations

There are several starting points for implementing multi-pathing:

  • In the Logical Volume Manager , a physical volume can be configured with several paths (for example under HP-UX with PV links )
  • in the block layer, e.g. B. under Linux in the Device Mapper
  • In the driver of the host bus adapter ( e.g. in the QLogic driver for Linux )
  • In the driver for hard disks (e.g. MPIO on AIX )
  • As an additional driver that makes new virtual hard disks visible to the operating system ( e.g. EMC Power Path with Power Devices )