A fault tolerant method transforms physically contiguous data in-place on a disk by partitioning the physically contiguous data into an empty region physically adjacent to data regions including a first data region and a last data region, the first and last data regions at opposing ends of the physically contiguous data regions. The physically contiguous data are transformed in an order beginning with the first data region and ending with the last data region. The transforming step perform first locking and reading the first data region, second, transforming the first data region, third, writing and unlocking the transformed first data region to the empty region, and fourth, declaring the first data region as the empty region while declaring the empty region as the first region. The first through fourth steps are repeated for each data region, until completion, to transform the physically contiguous data in-place on the disk.