Figure 78 Split mirror backup concept
The target volumes in replica are typically connected to a separate client, which also has tape devices connected to allow for local backup. Usually, hardware mirror technologies such as HP StorageWorks Disk Array XP or EMC Symmetrix are used to create a replica such as:
•HP StorageWorks ContinuousAccess XP or
•HP StorageWorks BusinessCopy XP
The availability of the application remains almost permanent, with the exception of a short period of time (lasting several seconds to a few minutes). This time is needed to make the data on the disk consistent and perform the actual split of the mirrors. The data must be consistent so that the application can make use of the data after a restore. Normally, the replica is not created at the time of backup, but is already available and synchronized to provide high availability to the application. The backup and the resyncing of the replica does not affect the application performance, since this occurs in parallel on separate hardware.
As the application client and backup client are different (in most cases), it is very important that all cached information (database cache, filesystem cache) on the client is flushed to the disk before the backup mirror is split off. One of the following options can achieve this:
266 | Split mirror concepts |