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If the nodes go offline or the storage at either site goes offline, leaving an online and accessible up-to-date copy, the HyperSwap function can automatically fail over access to the online copy. The HyperSwap function also automatically resynchronizes the two copies when possible. 

HyperSwap capability enables each volume to be presented by two I/O groups. The configuration tolerates combinations of node and site failures, by using the same flexible choices of host multipathing driver interoperability that are available for the IBM Storwize. The use of FlashCopy helps maintain a golden image during automatic resynchronization. 

Important:  Because Remote Mirroring is used to support the HyperSwap capability, Remote Mirroring licensing is a requirement for using HyperSwap. 

The HyperSwap function uses a hyperswap topology by spreading the control enclosure of the system across two sites, with storage at a third site that acts as a tie-breaking quorum device. Consider the following points: 

GLYPH<SM590000> The HyperSwap topology requires at least one control enclosure in each main data site. Therefore, to get a volume that is resiliently stored on both sites, one control enclosure with the necessary storage capacity is required. 

GLYPH<SM590000> The HyperSwap topology uses more system resources to support a fully independent cache on each site, which provides full performance, even if one site is lost. 

GLYPH<SM590000> The HyperSwap function can be configured by using the GUI or command-line interface (CLI). 

GLYPH<SM590000> The hosts, Storwize V5000 control enclosures, and Storwize V5000 storage enclosures are in one of two failure domains or sites. External virtualized storage capacity can also be used. 

GLYPH<SM590000> Volumes are visible as a single object across both sites (the Storwize V5000 control enclosure). 

At least two control enclosures are required for HyperSwap. System scalability depends on the hardware details, as listed in Table 10-12. 

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So, a V5000 HyperSwap cluster is always restricted to a single control enclosure per site. The Storwize V7000 and IBM SAN Volume Controller can provide more scalability and offer more flexibility. 

