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Multiplexing Guidelines
For striped data
- Disable for striped data
- Set MAXOPENFILES 1 or FILESPERSET 1
- RMAN allocates “n” buffers
- RMAN issues “n” parallel reads
- So you really get built-in multiple reads
- Just not commingled blocks from different datafiles
For non-striped data
- Maximum 4 – 8, but must test!
Notes:
When your data is striped (according to the SAME methodology) it is best to disable or severely limit RMAN multiplexing. The reason is that the striping causes RMAN to automatically allocate some number of buffers, equal to the number of stripes, and issue the same number of read I/O requests. Thus, in essence, we get a sort-of multiplexing: RMAN issues parallel reads to different disk devices, just not to different datafiles.