Occasionally I'll hear the idea that asynchronous array-level replication does not effect primary system performance. That's just not true. It doesn't effect performance in the same way as synchronous replication does. But that's different from not affecting primary system performance at all*.
But why take my word from it? EMC and Hitachi are both really good at array level replication. I've already quoted from EMC documentation on my blog today, so now I'll switch to Hitachi documentation :-)
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Hitachi Virtual Storage Platform
Hitachi Universal Replicator User Guide
www.hds.com/assets/pdf/vsp-hitachi-universal-replicator-user-guide.pdf
Performance is affected because of journal-to-journal copying. Usage rates are also affected.
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*It is possible that a database with asynchronous writes and a light enough level of writes may see the effects of asynchronous - even synchronous - array replication without noticeably impeding query completion speed. But I'm talking about pedal-to-the-metal data warehouse loads and the like :)
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