
338 High Performance Parallel I/O
plain disks. OSDs differ in that they typically offer byte access granularity (as
opposed to sector granularity). The OSD implements the storage operations
(data transfer and layout), without defining any policy.
Many parallel file system implementations today, while exporting a mostly
POSIX-compliant model to their clients, internally access local storage using
an object storage model similar to the T10 standard [6, 7, 19, 18]. Unfortu-
nately, as seen with MPI-IO, these object storage abstractions are frequently
built on top of an existing local POSIX file system. This means potential effi-
ciency gains (for example, in