Overview of Global Mirror
The IBM® DS8700 storage subsystem provides asynchronous mirroring using the Global Mirror feature. Global Mirror is implemented through a combination of FlashCopy® functions, Global-Copy functions, and Sessions functions to achieve consistency in the context of asynchronous replication.
- FlashCopy
- A technology offered by all enterprise storage systems that allows users to create near-instantaneous copy of a physical volume. The instantaneous copy is handled by copying data in the background while allowing the source and target volumes to be read and written. While the background copying is in progress, all writes to the source volume are handled by the storage system by first copying the old block to the target volume. This process only occurs if the corresponding block on the target has not already been modified. Once the background copying completes, both source and target volumes, are exact copies of the last time the FlashCopy command was issued.
- Global Copy
- A DS8000® technology that allows data to be mirrored to another storage unit in an asynchronous manner, without giving any guarantees about the order of data replication. Data can appear on the recovery site out-of-order. This is a good option for any application that wants to handle disaster recovery, but can tolerate out-of-order data.
- Sessions
- A mechanism by which a DS8000 Series storage system coordinates the replication process with the storage systems on the recovery site. When the Sessions function is used with the FlashCopy function and the Global Copy function you can achieve asynchronous replication while maintaining consistency properties.