Hardware Reference
In-Depth Information
FIGURE 24.1: Application access patterns for moving data between memory
and a file.
writes and reads, the amount of data read and written, and whether the data
is strided or sequential in a file.
At NERSC, the IOR benchmark is used for procuring and testing new sys-
tems, as well as measuring the performance of the file system over the lifetime
of a system. A number of different IOR tests are used to gauge the perfor-
mance and health of the file system. Tests include small block I/O, where an
I/O transaction size (the amount of data transferred to disk at a given time)
is significantly less than the lock size on the file system. This measures the file
system's capabilities aggregating small transactions, as well as measuring lock
contention overhead. The small block I/O tests are performed using differ-
ent I/O APIs, namely POSIX file-per-processor I/O, in addition to MPI-IO.
Running the same test, but only altering the I/O API allows overhead from
MPI-IO to be measured. These same tests are performed using large block
I/O where the I/O transaction size is equal to or greater than the lock size of
the le system, typically 1{4 MB.
The IOR benchmark returns the aggregate write and read rate in the
output of the test. These numbers can also be verified by monitoring the
