Relocating Bad Blocks

The physical layer of the LVDD checks each physical request to see if there are any known software-relocated bad blocks in the request. The LVDD determines if a request contains known software-relocated bad blocks by hashing the physical address. Then a hash chain of the LVDD defects directory is searched to see if any bad-block entries are in the address range of the request.

If bad blocks exist in a physical request, the request is split into pieces. The first piece contains any blocks up to the relocated block. The second piece contains the relocated block (the relocated address is specified in the bad-block entry) of the defects directory. The third piece contains any blocks after the relocated block to the end of the request or to the next relocated block. These separate pieces are processed sequentially until the entire request has been satisfied.

Once the I/O for the first of the separate pieces has completed, the iodone kernel service calls the LVDD physical layer's termination routine (specified in the b_done field of the buf structure). The termination routine initiates I/O for the second piece of the original request (containing the relocated block), and then for the third piece. When the entire physical operation is completed, the appropriate scheduler's policy routine (in the second layer of the LVDD) is called to start the next phase of the logical operation.