Disk Interleaving and Very Large Fast Fourier Transforms

Disk interleaving (disk striping) distributes fragments of a data block across a group of disks. For applications with regular I/O reference patterns and requiring large block transfers, interleaving can speed data transfers and reduce I/O times. Com puting fast Fourier transforms is one such application; the algorithm assumes that the entire array to be transformed should fit in the main memory. Occasionally arrays exceed the capacity of the main memory and reside in secondary storage. We have used synchronous and asynchronous disk striping to compute very large three-dimensional FFTs. We present a two-pass algorithm for com puting data stored on interleaved disks and analyze the I/O times. A large FFT ex ample provides a quantitative view of the advantages of disk interleaving for this application.