High availability concepts

iSeries™ and xSeries® integration and storage virtualization provide innovative options that can enable you to enhance the reliability and recoverability of your Windows server environment. Hosted systems can provide increased availability with one or more of the following technologies.

Hot spare hardware

Hot spare hardware provides a way to quickly recover from certain types of hardware failures. This can reduce the server downtime from hours or days to minutes. With hosted systems, there are two ways to use hot spare hardware to minimize downtime that is caused by hardware failures:

1. Hosted system hardware, including Integrated xSeries Servers, xSeries servers that are attached via an Integrated xSeries Adapter, and xSeries or IBM® BladeCenter™ servers that are attached via an iSCSI host bus adapter, can be hot spared. If the hardware that is used to run the hosted system fails, you can quickly switch the hosted system's disk images to compatible spare hardware and restart the hosted system. For more information, see Hot spare between server hardware.
2. For iSCSI attached servers, the iSeries target iSCSI host bus adapters (iSCSI HBA) can be hot spared. If an iSCSI HBA that a hosted system is using fails, you can quickly switch the hosted system to use a spare iSCSI HBA and restart the hosted system. For more information, see Hot spare between iSCSI local host adapters.

iSCSI multi-path

A hosted system can use redundant iSCSI data paths to access virtual disks hosted by i5/OS™. This is accomplished by defining a group of two or more iSCSI HBAs and then specifying that a given virtual disk should be accessed using a group, rather than a single iSCSI HBA. With this configuration, the data on the virtual disk can be accessed using any of the iSCSI HBAs in the group.

One advantage of the multi-path configuration is that if one of the iSCSI HBAs in the multi-path group fails, the hosted system can continue to access the disks that are configured to use the multi-path group uninterrupted, using any of the other iSCSI HBAs that are configured in the multi-path group. For more information, see Advanced iSCSI support.

Microsoft® Windows Cluster Service (MSCS)

Hosted servers can use MSCS to provide real-time application failover in the case of hosted system hardware or software failures. User-initiated failovers can be used to take a server offline so that maintenance or backups can be performed while the application continues to run on the other server(s) in the cluster. For more information, see Windows Cluster Service.