Enhanced_concurrent_mode

AIX® provides a new form of concurrent mode: enhanced concurrent mode. In enhanced concurrent mode, the instances of the Concurrent Logical Volume Manager (CLVM) coordinate changes between nodes through the Group Services component of the Reliable Scalable Cluster Technology (RSCT) facility in AIX.

Group Services protocols flow over the communications links between the cluster nodes. Support for enhanced concurrent mode and prior concurrent mode capabilities has the following differences:

• Any disk supported by HACMP™ for attachment to multiple nodes can be included in an enhanced concurrent mode volume group; the special facilities of SSA disks are not required.
• The same capabilities for online changes of volume group and logical volume structure that have always been supported by AIX for SSA concurrent mode volume groups are available for enhanced concurrent mode volume groups.

Keep in mind the following when planning an HACMP environment:

• When concurrent volume groups are created on AIX, they are created as enhanced concurrent mode volume groups by default.
• SSA concurrent mode is no longer supported by AIX. HACMP will automatically convert them to enhanced concurrent mode the first time they are varied on.
• If one node in a concurrent resource group runs a 64-bit kernel, then it must use an enhanced concurrent mode volume group.
• SSA concurrent mode is not supported on 64-bit kernels.
• SSA disks with the 32-bit kernel can use SSA concurrent mode.
• The C-SPOC utility does not work with RAID concurrent volume groups. You need to convert them to enhanced concurrent mode (otherwise, AIX sees them as non-concurrent).
• The C-SPOC utility does not allow you to create new SSA concurrent mode volume groups. HACMP will automatically convert these volume groups to enhanced concurrent mode the first time they are varied on.
• You can include enhanced concurrent mode volume groups into shared resource groups. HACMP lists them in volume group picklists in resource group configuration SMIT panels. When enhanced concurrent volume groups are used in a non-concurrent environment, the volume groups are not concurrently accessed, they are still accessed by only one node at any given time.
• You can turn volume groups that are enhanced concurrent into geographically mirrored volume groups, if you have installed HACMP/XD for GLVM.

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