I may be wrong, but I think the swap to a reserved sector only happens on a write operation. So reads will fail until you attempt to write back at which point future reads will succeed. With RAIDframe, the initial read failure fails the whole component and no writeback is automatically attempted (too bad as it could just copy from the rest of the array).
So if you know failed sector numbers, you could reallocate them by using dd if=/dev/zero seek=N count=1 (where N is the sector number) and then re-fsck.
If using RAIDframe, usually just the rebuild of the RAID array with -R is sufficient.