CBC mode and its relatives, one of which is likely the mode you have in your head, is great for an ephemeral stream, but not well suited to permanent storage: it's inappropriate for hard drives because it forbids random access, and it's inappropriate for tape drives because it makes the tape too lossy.<p>Real disks use either CTR mode or CFB mode, neither of which has those two problems.<p>CFB mode depends only on the previous cyphertext block to decode the current block, which allows random access but amplifies a one-bit error to a one-block error.  CTR mode uses the current logical block number as IV salt, so it's both random access and minimally-corrupting in the case of errors.  AFAIK most real-world hard drive encryption uses CTR mode, precisely to avoid the problem that concerns you.