Řeší se to tak, že se pomocí CBC šifrují jednotlivé sektory, a to odděleně. Cituji:
Since CBC encryption is a recursive algorithm, the encryption of the n-th block requires the encryption of all preceding blocks, 0 till n-1. Thus, if we would run the whole hard disk encryption in CBC mode, one would have to re-encrypt the whole hard disk, if the first computation step changed, this is, when the first plain text block changed. Of course, this is an undesired property, therefore the CBC chaining is cut every sector and restarted with a new initialisation vector (IV), so we can encrypt sectors individually. The choice of the sector as smallest unit matches with the smallest unit of hard disks, where a sector is also atomic in terms of access.
Zdroj: Clemens Fruhwirth, Linux hard disk encryption settings