IBM AIX Continuous Availability Features - IBM Redbooks

Note: This is not to be confused with authorization (granting or denying access to
resources), which is handled by RMC.
Cluster Security Services uses credential-based authentication that enables:
► A client process to present information to the server that owns the resource to be
accessed in a way that cannot be imitated.
► A server process to clearly identify the client and the validity of the information.
► Credential-based authentication uses a third party that both the client and the server trust.
Group Services and Topology Services subsystems
Group Services and Topology Services, although included in RSCT, are not used in a
management domain structure. These two components are used in high availability clusters
for complete high availability and disaster recovery solutions, such as High-Availability
Cluster Multi-Processing (HACMP), providing node and process coordination and node and
network failure detection.
These services are often referred to as hats and hags: high availability Topology Services
daemon (hatsd) and Group Services daemon (hagsd).
Additional detailed information about IBM Reliable Scalable Clustering Technology is
available in Reliable Scalable Cluster Technology: Administration Guide, SA22-7889.
2.1.11 Dual IBM Virtual I/O Server
Dual IBM Virtual I/O Server (VIOS) provides the capability for a single physical I/O adapter to
be used by multiple logical partitions of the same server, thus allowing consolidation of I/O
resources and minimizing the number of I/O adapters required. The IBM Virtual I/O Server is
the link between the virtual resources and physical resources. It is a specialized partition that
owns the physical I/O resources, and runs in a special partition that cannot be used for
execution of application code. It mainly provides two functions:
► Serves virtual SCSI devices to client partitions
► Provides a Shared Ethernet Adapter for VLANs
While redundancy can be built into the VIOS itself with the use of standard AIX tools like
multipath I/O (MPIO) and AIX Logical Volume Manager (LVM) RAID Options for storage
devices, and Ethernet link aggregation for network devices, the Virtual I/O Server must be
available with respect to the client. Planned outages (such as software updates) and
unplanned outages (such as hardware outages) challenge 24x7 availability. In case of a
crash of the Virtual I/O Server, the client partitions will see I/O errors and not be able to
access the adapters and devices that are hosted by the Virtual I/O Server.
The Virtual I/O Server itself can be made redundant by running a second instance in another
partition. When running two instances of the Virtual I/O Server, you can use LVM mirroring,
multipath I/O, Ethernet link aggregation, or multipath routing with dead gateway detection in
the client partition to provide highly available access to virtual resources hosted in separate
Virtual I/O Server partitions. Many configurations are possible; they depend on the available
hardware resources as well as on your requirements.
For example, with the availability of MPIO on the client, each VIOS can present a virtual SCSI
device that is physically connected to the same physical disk. This achieves redundancy for
the VIOS itself and for any adapter, switch, or device that is used between the VIOS and the
disk. With the use of logical volume mirroring on the client, each VIOS can present a virtual
SCSI device that is physically connected to a different disk and then used in a normal AIX
Chapter 2. AIX continuous availability features 17