Strategies for Data Protection - Brocade

Highly Available StorageFigure 8. Array-based (top) and server-based (bottom) disk mirroringAlthough simple mirroring accomplishes the goal of protecting dataagainst disk failure, additional utilities are required to reconstitute theprimary disk set and re-establish the mirror operation. Once the failedprimary has been serviced, for example, the data on the primary mustbe rebuilt and synchronized to the new production mirror. For arraybasedmirroring, this is typically performed as an automatic backgroundoperation and once synchronization has been achieved, theprimary is reinstated. This automated process, however, can haveunintended consequences. In one customer case study, a service callto replace a drive on a mirror inadvertently resulted in a drive on theprimary being swapped. Instead of failing over to the mirror image, themirror was rebuilt to the now-corrupted primary image. It is no greatmystery that tape backup endures as a data protection insurance policyagainst potential array failures.The primary drawback to mirroring within an array is that the entirearray is subject to failure or outage. Consequently, data centers mayphysically isolate primary and mirror arrays, placing them in separateareas with separate power sources.Strategies for Data Protection 17