Without writing a magnum opus on the topic one of the features I really like in the new DDOS 5.3 release for Data Domain systems is the ability to deduplicate multiplexed Oracle RMAN backup streams.
Multiplexing as a backup concept is a hold over from the days when you needed to keep tape drives writing data at a minimum throughput to prevent rewind operations from occurring. You did this by interleaving backups from different systems, queuing up the writes and sending them all to the same tape drive. Net result you kept the tape drive fed during write but the restore speed was significantly lower due to seek operations to read the interleaved fragments back. Disk eliminated the need for multiplexing.
Oracle DBAs, having to maintain overall system responsiveness, have a different set of issues and juggle channels, disk buffers and data rate transmission when it comes to moving as many database files to a backup target as quickly as they can. The result of this means as they balance the resources available to them it can lead to a multiplexing situation where multiple reads are combined into an interleaved write as that’s the best use of their available system I/O.
Multiplexing, like compression or encryption is awful for data deduplication but unlike either of those it isn’t down to re-encoding the information or eliminating commonality, it’s a direct result of the metadata inserted in amongst the files that have been interleaved together. The metadata causes the deduplication ratio to fall when the deduplication system fails to identify it as something apart from, not in, the database files themselves.
In DDOS 5.3 however the Data Domain operating system can identify all this metadata as being separate from the database files and therefore provide a backup deduplication ratio on par with a non-multiplexed backup of the same information.
And I think that’s pretty cool.