One of the most powerful features of the EMC DL3D is its ability to do both in-line and post-process deduplication. It is one of the few (the only?) deduplication appliance that offers users this flexibility, and in fact lets you do both on one appliance, depending on the requirements of the data being backed up.
Certain competitors have done their best to portray this flexibility as a weakness. Huh? Since when is choice a bad thing?
Well, it isn't a bad thing at all. Choice is good. Flexibility is good.
The other criticism that gets leveled against the DL3D here is that the in-line is not really in-line. In particular, Data Domain attempts to claim that EMC doesn't do in-line deduplication at all--that we write to a disk cache, and that this lets us be deceptive with our performance numbers.
Nothing could be more misleading.