If a managed disk (MDisk) logical unit (LU) is accessible
through multiple storage systems ports, the Lenovo Storage V7000 system
ensures that all nodes that access this LU coordinate their activity
and access the LU through the same storage systems port.
Monitoring LU access through multiple storage systems ports
When the Lenovo Storage V7000 system
can access an LU through multiple storage systems ports, the system uses the following criteria to determine
the accessibility of these ports:
- The Lenovo Storage V7000 node is a member of a clustered system.
- The Lenovo Storage V7000 node has Fibre Channel connections
to the storage systems port.
- The Lenovo Storage V7000 node has successfully discovered the LU.
- Slandering has not caused the Lenovo Storage V7000 node
to exclude access to the MDisk through the storage systems port.
An MDisk path is presented to the clustered system for all Lenovo Storage V7000 nodes
that meet these criteria.
Storage-system port selection
When an MDisk
is created, Lenovo Storage V7000 selects
one of the storage system ports to access the MDisk.
Table 1 describes
the algorithm that
Lenovo Storage V7000 uses
to select the
storage system port.
Table 1. Storage system port selection algorithm
| Criteria |
Description |
| Accessibility |
Creates an initial set of candidate storage-system
ports. The set of candidate storage-system ports include the ports
that are accessible by the highest number of nodes. |
| Slandering |
Reduces the set of candidate storage-system
ports to those with the lowest number of nodes. |
| Preference |
Reduces the set of candidate storage-system
ports to those that the storage system uses as preferred ports. |
| Load balance |
Selects the port from the set of candidate storage-system
ports that has the lowest MDisk access count. |
After the initial device port selection is made for
an MDisk, the following events can cause the selection algorithm to
rerun:
- A new node joins the system and has a different view of the storage system than the other nodes in the system.
- The detectmdisk command-line interface (CLI)
command is run or the Discover MDisksmanagement GUI function is used. The detectmdisk CLI command
and the Discover MDisks function have the system
rescan the Fibre Channel network.
The rescan process discovers any new MDisks that might have been added
to the system and rebalances MDisk access across the available storage system ports.
- Error recovery procedures (ERPs) are started because a storage system has changed its preferred port.
- New storage system ports are discovered for the storage system that is associated with the MDisk.
- The storage system port that is currently selected becomes inaccessible.
- Slandering has caused Lenovo Storage V7000 to
exclude access to the MDisk through the storage system port.