One of the options for taking DB2 backups is to split mirrored disks. However this is not supported in the IBM Smart Analytics System (ISAS) and Infosphere Balanced Warehouse (IBW) solutions which use RAID-6 for data storage instead of mirrored drives.
If node failover occurs while a split mirror backup is in progress, Tivoli System Automation (TSA) will not restart the database correctly on the newly online node.
The steps for taking a "split mirror" DB2 backup are detailed here:
The issue is that prior to splitting the pair of mirrored disks (or taking a flash copy if the disks where the database data resides are not mirrored all the time) the DBA will have to issue this command to suspend DB2 write activity:
db2 set write suspend for database
TSA manages failovers to/from standby nodes in cluster environments like those used in BW and ISAS. If a node is failed over (manually or automatically triggered) while DB2 database writes are suspended, TSA will not restart DB2 correctly on the new active node because it will not know that it needs add the keywords 'write resume' to the 'db2 restart database' statement. A manual restart of DB2 with the correct options will therefore be required.
Resolving the problem
The best solution for ISAS/IBW environments is to use a DB2 backup strategy that does not need database writes to be suspended, such as the default of using Tivoli Storage Manager (TSM).
If the customer must use a split mirror style of backup, then they could set TSA into manual mode while the backups are running. This will prevent TSA from from doing an automatic failover and restart. However, the reason for having TSA installed is to have it automatically ensure 24x7 uptime or as close as it can achieve it, so disabling it on a regular basis seems counter intuitive. Someone would have to monitor the system while the backup was running, and they are usually scheduled for an inconvenient hour of night.
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