SirHumphreyAppleby:
There may be some additional resources used in order to flag blocks encrypted with Blowfish vs AES, but there must already be headers for blocks as encryption and compression can be disabled on archives. Seems improbable they wouldn't have a free bit somewhere in the headers in order to flag Blowfish/AES. The limit therefore appears to be entirely arbitrary.
I believe the technical platform constraint is that they are hoping people with larger backups go elsewhere. Last year they changed the definition of commercially reasonable for the multi-computer Home plan from 20TB to 5TB. I note the CrashPlan for Small Business terms now state e.g. 5TB, while the Home terms said i.e. 5TB (previously 20TB). That's quite a significant change in definition. Sneaky.
They didn't say it had anything to do with the Blowfish/AES issue. I imagine much more likely it has to do with however the storage works on their end on either or both sides. Maybe something like if you have more than 5TB, it's in multiple parts at some level. I'm sure they could have found a solution if they tried hard enough and probably the fact they'd prefer people with such large backups to go elsewhere is a factor, but I wouldn't be surprised if there really is a techical reason for it.



