If you're storing A, B, and A+B, and then the file holding block A is deleted, what happens? You can't immediately remove A, because then you lose the redundanc

If you're storing A, B, and A+B, and then the file holding block A is deleted, what happens? You can't immediately remove A, because then you lose the redundancy for B. You'd need to somehow find a _new_ pair for B, C (maybe of another block in the same situation, where D is supposed to be deleted?), and write B+C, then delete A, A+B, D, C+D. Pretty fiddly.