When a database is mirrored using the mirroring facility of LVM or the device driver, the duplicate volume may not match the original volume if an error occurs in the OS or server machine while the database is being copied or if the device driver shuts down input/output during a system switchover. This is called a mismatch between the original and the mirror duplicate. When it occurs, you use one of the following methods to eliminate the mismatch:
Method 1 is usually used. You use method 2 when it is not possible to use the LVM or device driver's facility to eliminate the mismatch, or when the process of matching the original and duplicate volumes takes too long and, as a result, a system requirement, such as system switchover time, cannot be satisfied.
Figure 18-8 shows an example of a system configuration when the rapid system switchover facility is used in an environment in which the LVM mirroring facility is used to mirror the database.
In this example, the full recovery processing performed by HiRDB during a restart is used to eliminate a mismatch between the original and the mirror duplicate.
Figure 18-8 Example of a system configuration in which the rapid system switchover facility is used
Figure 18-9 shows an example of a system configuration when the rapid system switchover facility is used in an environment in which the mirroring facility of Hitachi Disk Array Driver for AIX is used to mirror the database.
In this example, the full recovery processing performed by HiRDB during a restart is used to eliminate a mismatch between the original and the mirror duplicate.
Figure 18-9 Example of a system configuration in which the rapid system switchover facility is used (for AIX 5L V5.2 or later)
Also use the mirroring facility of Hitachi Disk Array Driver for AIX to mirror the disk in which the HiRDB file system area for RDAREAs is located, as shown in Figure 18-10. Mirror both the primary and secondary systems.
Figure 18-10 Example of a disk configuration in which the system switchover facility is used (for AIX 5L V5.2 or later)
If an error occurs in the OS or server machine while the database is being copied or if system switchover occurs, mismatch may occur between the original and the mirror duplicate. However, the full recovery processing performed by HiRDB during a restart will make the original and the mirror duplicate match in terms of RDAREAs. Thus, there is no need to make the original and duplicate volumes match before restarting HiRDB.