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Upgrading to DAOS Version 2.0

DAOS Version 2.0 is a major feature release, and it was a conscious design decision to not provide backwards compatibility with previous DAOS releases in favor of new feature development and stabilization. For future DAOS releases, a limited form of backward compatibility between two adjacent releases is planned.

DAOS Version 2.0 introduces several protocol and API changes, as well as changes in the internal object layout, which make DAOS Version 2.0 incompatible with previous DAOS releases. It is therefore not possible to perform online or offline upgrades from previous DAOS releases to DAOS Version 2.0, while maintaining the user data in containers that have been created with previous DAOS releases.

This means that an upgrade from DAOS Version 1.0 or 1.2 to DAOS Version 2.0 is essentially a new installation. Existing user data in DAOS should be backed up to non-DAOS storage before the upgrade, as the DAOS storage will need to be reformatted. For POSIX containers, there are two paths to perform such a backup:

  1. On a DAOS client where the DAOS POSIX container is dfuse-mounted, the serial Linux cp command can be used to copy out the data. To improve throughput, it is adviable to use the DAOS I/O interception library. Running LD_PRELOAD=/usr/lib64/ cp $SOURCE $DEST will provide significantly better performance than just running cp $SOURCE $DEST.

  2. For larger data volumes, the MPI-parallel tools from mpiFileUtils can be used. Note that the DAOS backend for mpiFileUtils was only added in DAOS Version 2.0. So for the purpose of backing up data from DAOS Version 1.0 or 1.2 containers, it is best to build mpiFileUtils without DAOS support. The dcp parallel copy command can then be run in its normal POSIX mode on the DAOS POSIX container, which needs to be dfuse-mounted on all nodes on which the MPI-parallel dcp job is run. Similar to the serial cp case, it is advisable to use dcp in conjunction with the DAOS I/O interception library to achieve higher throughput. To do this, the LD_PRELOAD setting must be passed to all tasks of the MPI-parallel job, for example with mpirun -genv LD_PRELOAD /usr/lib64/ -np 8 -f hostfile dcp $SOURCE $DEST.

When planning the upgrade to DAOS Version 2.0, please also verify the supported operating system levels as outlined in the DAOS Version 2.0 Support document. If an OS upgrade is required, this should be performed prior to upgrading DAOS.


Note that CentOS 8.3 uses hwloc-1.11, while CentOS 8.4 uses hwloc-2.2. DAOS requires the hwloc-1 functionality, and DAOS Version 2.0 includes the compat-hwloc1 RPM that addresses this version change. Older DAOS releases do not include this compatibility package. So updating CentOS 8.3 to CentOS 8.4 while an older DAOS release is installed will likely fail with a dependency error. Adding the DAOS 2.0 packages repository and updating DAOS to Version 2.0 at the same time as performing the CentOS update should eliminate this problem.

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