This paper discusses our implementation of Rajasekaran\u27s (l,m)-mergesort algorithm (LMM) for sorting on parallel disks. LMM is asymptotically optimal for large problems and has the additional advantage of a low constant in its I/O complexity. Our implementation is written in C using the ViC* I/O API for parallel disk systems. We compare the performance of LMM to that of the C library function qsort on a DEC Alpha server. qsort makes a good benchmark because it is fast and performs comparatively well under demand paging. Since qsort fails when the swap disk fills up, we can only compare these algorithms on a limited range of inputs. Still, on most out-of-core problems, our implementation of LMM runs between 1.5 and 1.9 times faster than qsort, with the gap widening with increasing problem size
