The goal of the simultaneous-write function is to minimize the amount of time that is required for storage-pool backup operations. IBM® Tivoli® Storage Manager provides several options for accomplishing this goal. Your choice depends on how you want to manage your environment.
You can specify the simultaneous-write function for a primary storage pool if it is the target for client store sessions, server import processes, or server data-migration processes. You can also specify the simultaneous-write function for a primary storage pool when it is the target for all of the eligible operations.
Writing data simultaneously during client store sessions might be the logical choice if you have sufficient time for mounting and removing tapes during the client store session. However, if you choose this option you must ensure that a sufficient number of mount points and drives are available to accommodate all the client nodes that are storing data.
As a best practice, you are probably issuing the BACKUP STGPOOL and COPY ACTIVEDATA commands for all the storage pools in your storage pool hierarchy. If you are, and if you migrate only a small percentage of data from the primary storage pool daily, writing data simultaneously during client store sessions is the most efficient option. This method is efficient because data is stored in copy storage pools and active-data pools when the client stores the data. Little or no data is left to copy during backup storage pool or copy active-data operations.
Writing data simultaneously during server data-migration processes is another option. It is the most efficient method of writing data simultaneously if you migrate all the data in your primary storage pool nightly and then back up the primary storage pools. The reason for the efficiency is that data written simultaneously to copy storage pools or active-data pools during migration is not copied during backup storage pool or copy active-data operations.
Use the simultaneous-write function during migration if you have many client nodes and the number of mount points that are required to write data simultaneously during client store sessions is unacceptable. Similarly, mounting and removing tapes when writing data simultaneously during client store sessions might be taking too much time. If so, consider writing data simultaneously during migration.
Another option is to specify the simultaneous-write function for a primary storage pool if it is the target for any of the eligible operations (client store, server import, server migration). This choice is preferable if, for example, you have large files to back up (for example, image files, database backup files, or Tivoli Data Protection files). Instead of backing up these files to the random-access disk storage pool at the top of the storage hierarchy, you can back them up to the sequential-access disk storage pool that is the next storage pool in the hierarchy. If you specify the simultaneous-write function for any of the eligible operations for the next storage pool, the following events occur:
By default, the Tivoli Storage Manager server writes data simultaneously during client store sessions if you have copy storage pools or active-data pools defined to the target storage pool.
You can also disable the simultaneous-write function. This option is useful if you have copy storage pools or active-data pools defined, but you want to disable the simultaneous-write function without deleting and redefining the pools.