Expert Oracle Exadata - Parent Directory

CHAPTER 13 MIGRATING TO EXADATAWhen to Use ASM RebalanceASM Rebalance is an excellent way of leveraging ASM’s built-in features to migrate your database withnear zero downtime. It is not the fastest way to migrate to Exadata, and there are a lot of very strictconfiguration requirements, but once the system is configured the migration is fairly automated. It isprobably the most reliable and error free method for migrating your database to Exadata.What to Watch Out for when Using the ASM Rebalance StrategyThis strategy is not well used or well documented. And it is not for the faint of heart (and certainly not forthe inexperienced system administrator). It requires strong system administration skills and solid Linuxsystems experience. Some of the preliminary steps, such as installing and configuring the InfiniBandcard and proper RDS/OFED drivers, can be disruptive to production uptime requirements. This methoddoes not create a copy of your database. It migrates your current database at the storage level. As such,storage layout changes like extent sizing, partitioning, and HCC compression must be done postmigration.A downside to the ASM rebalance method is that ASM Allocation Units (AUs) cannot bechanged after the disk group is created. Exadata is more efficient at scanning 4MB AUs, so if your diskgroups were configured with 1MB AUs, you would eventually want to create new disk groups in Exadatawith 4MB AU sizes and migrate your database to them.Post-Migration TasksBecause ASM rebalance makes no changes to the database, tasks like resizing extents, partitioning largetables, and compressing tables will all have to be done post-migration. This can be a substantial task thattakes anywhere from several days to several weeks to complete. For all physical migration strategiesexcept TTS, you will need to perform some post-migration steps to add the database into the ClusterReady Services configuration. There is nothing Exadata-specific to this process (other than connecting tothe storage cells), it is the same as for any 11gR2 database. The process is well documented andexamples are easy to find, so we won’t go into the details here, but the basic steps are as follows:1. Set the following instance parameters in the spfile:• *.cluster_database=true• *.cluster_database_instances=2• NEW_PROD1.instance_name=NEW_PROD1• NEW_PROD2.instance_name=NEW_PROD2• NEW_PROD1.instance_number=1• NEW_PROD2.instance_number=2• NEW_PROD1.thread=1• NEW_PROD2.thread=2• NEW_PROD1.undo_tablespace=undo_tbs1• NEW_PROD2.undo_tablespace=undo_tbs2463