Announcing IBM High Availability
Customers have asked for an end-to-end high-availability solution from IBM, and it delivers with HASM.
Illustration by Art Valero
IBM* High Availability Solutions Manager (HASM) represents a milestone marking more than a decade of high-availability (HA) R&D in the IBM Rochester development lab. The new product, announced Jan. 29, went GA on March 21.
IBM customers have long asked for a total IBM HA solution to help provide near-continuous application service, help eliminate the impact of planned and unplanned outages, and support regular and sustained role-swap operations. IBM responded with a series of HA releases in i5/OS*:
- V4R4 introduced Cluster Resource Services.
- V5R1 offered independent auxiliary storage pools (IASPs) for IFS objects.
- V5R2 extended IASP support to library-based objects.
- V5R3 delivered cross-site mirroring (XSM) architecture with geographic mirroring.
- V5R4 added the administrative domain to simplify synchronization of system objects.
- V6R1 adds the Metro Mirror and Global Mirror functions of the IBM System Storage* server interfaces to XSM.
IBM has now brought all of these HA technologies together under the HASM licensed program number 5761-HAS, providing the interfaces to configure and manage HA solutions and XSM technologies (see Figure 1).
The HASM Architecture
HASM combines several i5/OS and IBM System Storage components into one end-to-end HA solution. i5/OS provides the building blocks of switchable devices, IASPs, cluster resource groups (CRGs) and cluster administrative domain.
A switchable device is a collection of hardware resources such as disk units, communication adapters and tape devices that can be switched from one system to another. For data resilience, the disk units can be configured into a special class of auxiliary storage pool independent of a particular host system. The benefit of using IASPs for data resiliency lies in their operational simplicity. Role swapping or switching is relatively straightforward and quick. Another key benefit of using IASPs is zero-transmission latency, which can affect any replication-based technology. The major effort associated with this solution involves setting up the DASD configuration, data and application structure. Making an IASP switchable is relatively simple.
A CRG is an i5/OS system object that’s a set of cluster resources used to manage events that occur in a clustered environment. The CRG describes a recovery domain and supplies the name of the CRG exit program called when certain cluster events occur. CRGs define nodes in the recovery domain with specific roles of either primary or backup. The primary and backup nodes are available access points for cluster resources. However, only the primary node will be the active access point at a given time. Primary-backup models of CRGs are defined as data resilient, application resilient or device resilient. Data resiliency enables multiple copies of data to be maintained on more than one node in a cluster and enables the point of access to be changed to a backup node. Application resiliency enables an application program to be restarted on either the same or a different node in the cluster. Device resiliency enables a device resource to be moved (switched) to a backup node.
A cluster administrative domain is used to maintain a consistent operational environment across a subset of cluster nodes (systems or partitions) to ensure that a highly available application will behave as expected when it’s switched or failed over to backup nodes. A cluster administrative domain uses a peer CRG to identify resources that must remain consistent across the systems in an HA environment. It then monitors for changes to these resources and synchronizes the changes across the active domain to maintain the consistency of the operational environment.
The benefit of using IASPs for data resiliency lies in their operational simplicity. Role swapping or switching is relatively straightforward and quick.
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