HyperSwap function

The IBM® HyperSwap® function is a high availability feature that provides dual-site, active-active access to a volume. HyperSwap functions are available on systems that can support more than one I/O group.

HyperSwap volumes have a copy at one site and a copy at another site. Data that is written to the volume is automatically sent to both copies. If one site is no longer available, the other site can provide access to the volume.

To construct HyperSwap volumes, active-active relationships are made between the copies at each site. These relationships automatically run and switch direction according to which copy or copies are online and up to date. The relationships provide access to whichever copy is up to date through a single volume, which has unique ID. Relationships can be grouped into consistency groups just like Metro Mirror and Global Mirror relationships. The consistency groups fail over consistently as a group based on the state of all copies in the group. An image that can be used for disaster recovery is maintained at each site.

When the system topology is set to hyperswap, each node, controller, and host in the system configuration must have a site attribute set to 1 or 2. Both node canisters of an I/O group must be at the same site. This site must be the same site of the controllers that provide the managed disks to that I/O group. When managed disks are added to storage pools, their site attributes must match. This requirement ensures that each copy in a HyperSwap volume is fully independent and is at a distinct site.

The Small Computer System Interface (SCSI) protocol allows storage devices to indicate the preferred ports for hosts to use when they submit I/O requests. Using the Asymmetric Logical Unit Access (ALUA) state for a volume, a storage controller can inform the host of which paths are active and which ones are preferred. In a HyperSwap system topology, the system suggests that the host use local nodes over remote nodes. A local is a node that is configured at the same site as the host.