IPSec recommends rekeying SA's figuring in both time and amount of data sent. Even when using AES-256 in CBC mode, the key and IV commonly get re-negotiated after 100MB.
My case isn't using IPSec, the above is just for comparison.
Assuming a plaintext is encrypted and stored to disk using AES-256 in CBC mode, is there a maximum 'safe' size? Fear not, each plaintext gets its own randomly generated IV. I'm just having a hard time finding what the upper bound is for practicing safe encryption.