The Message Passing Interface (MPI) Standard, maintained by the MPI Forum, includes a chapter on MPI-IO.
ROMIO is a well-known implementation of MPI-IO and is included in many MPI implementations. DAOS provides its own MPI-IO ROMIO ADIO driver. This driver has been merged in the upstream MPICH repository, see https://github.com/pmodels/mpich/tree/main/src/mpi/romio/adio/ad_daos for details.
Starting with DAOS 1.1.3, the
--svc parameter (number of service replicas)
is no longer needed, and the DAOS API has been changed accordingly.
Patches have been contributed to MPICH that detect the DAOS API version
to gracefully handle this change, but those patches have not yet been
picked up in the MPI releases below. For details check the latest commits
MPI Implementations that support DAOS¶
Building MPICH with DAOS Support¶
To build MPICH, including ROMIO with the DAOS ADIO driver:
export MPI_LIB="" git clone https://github.com/daos-stack/mpich cd mpich ./autogen.sh mkdir build; cd build ../configure --prefix=dir --enable-fortran=all --enable-romio \ --enable-cxx --enable-g=all --enable-debuginfo --with-device=ch3:sock \ --with-file-system=ufs+daos --with-daos=/usr --with-cart=/usr make -j8; make install
This assumes that DAOS is installed into the
which is the case for the DAOS RPM installation.
In DAOS 1.0, CART was packaged separately from DAOS, and the
--with-cart option was needed to allow separate installation locations.
With DAOS 1.1 or higher, CART is included in the main DAOS packages
--with-cart option is no longer needed.
An MPICH pull request is in process to remove the option from the MPICH
configure step, but currently it is still required to build MPICH.
LD_LIBRARY_PATH to where you want to build your client
apps or libs that use MPI to the path of the installed MPICH.
Note that Intel MPI uses
libfabric (both 2019.8 and 2019.9 use
Care must be taken to ensure that the version of libfabric that is used is at a level that includes the patches that are critical for DAOS. DAOS 1.0.1 includes
libfabric-1.9.0, and the DAOS 1.1.2 pre-release
To use DAOS 1.1 with Intel MPI 2019.8 or 2019.9, the
is supplied by DAOS (and that is installed into
/usr/lib64 by default)
needs to be used by listing it first in the library search path:
The next Intel MPI release is expected to contain a version of
that includes all patches to work with DAOS.
It will then no longer be necessary to override the
libfabric version that is
shipped with Intel MPI by the version provided by DAOS.
Open MPI 4.0.5 does not yet provide DAOS support. Since one of its MPI-IO implementations is based on ROMIO, it will likely pick up DAOS support in an upcoming release.
MVAPICH2 2.3.4 does not yet provide DAOS support. Since its MPI-IO implementation is based on ROMIO, it will likely pick up DAOS support in an upcoming release.
Testing MPI-IO with DAOS Support¶
Build any client (HDF5, ior, mpi test suites) normally with the mpicc command and mpich library installed above (see child pages).
To run an example with MPI-IO:
- Create a DAOS pool on the DAOS server(s). This will return a pool uuid "puuid" and service rank list "svcl".
- Create a POSIX type container:
daos cont create --pool=puuid --type=POSIXThis will return a container uuid "cuuid".
- At the client side, the following environment variables need to be set:
export DAOS_POOL=puuid; export DAOS_SVCL=svcl; export DAOS_CONT=cuuid. Alternatively, the unified namespace mode can be used instead.
- Run the client application or test.
MPI-IO applications should work seamlessly by just prepending
daos:to the filename/path to use the DAOS ADIO driver.
Limitations of the current implementation include:
Reading Holes does not return 0, but leaves the buffer untouched.
No support for MPI file atomicity, preallocate, or shared file pointers.