Extend_Quantity=number-blocks

    Sets the size, in blocks, by which the backup file can be
    extended. The minimum value for the number-blocks parameter is
    1; the maximum value is 65535. If you do not specify the Extend_
    Quantity qualifier, the default number of blocks by which an
    on-disk backup file can be extended is 2048 blocks.

    This qualifier cannot be used with backup operations to tape.