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DAOS Version 2.6 Release Notes

We are pleased to announce the release of DAOS version 2.6.

DAOS Version 2.6.0 (2024-07-26)

General Support

DAOS Version 2.6.0 supports the following environments:

Architecture Support:

  • DAOS 2.6.0 supports the x86_64 architecture.

Operating System Support:

  • SLES/Leap 15 SP5
  • EL8.8/8.9 (RHEL, Rocky Linux, Alma Linux)
  • EL9.2 (RHEL, Rocky Linux, Alma Linux)

Fabric and Network Provider Support:

  • libfabric support for the following fabrics and providers:

    • ofi+tcp on all fabrics (without RXM)
    • ofi+tcp;ofi_rxm on all fabrics (with RXM)
    • ofi+verbs on InfiniBand fabrics and RoCE (with RXM)
    • ofi+cxi on Slingshot fabrics (with HPE-provided libfabric)

  • UCX support on InfiniBand fabrics:

    • ucx+ud_x on InfiniBand fabrics
    • ucx+tcp on InfiniBand fabrics

Storage Class Memory Support (PMem and non-PMem servers):

  • DAOS Servers with 2nd gen Intel Xeon Scalable processors and Intel Optane Persistent Memory 100 Series.
  • DAOS Servers with 3rd gen Intel Xeon Scalable processors and Intel Optane Persistent Memory 200 Series.
  • DAOS Servers without Intel Optane Persistent Memory, using the Metadata-on-SSD (Phase1) code path.

For a complete list of supported hardware and software, refer to the Support Matrix

Key features and improvements

Software Version Currency

  • See above for supported operating system levels.

  • Libfabric and MLNX_OFED (including UCX) have been refreshed. Refer to the Support Matrix for details.

  • The following prerequisite software packages that are included in the DAOS RPM builds have been updated:

    • Mercury has been updated to 2.3.1
    • Raft has been updated to 0.11.1-1.416
    • PMDK has been update to 2.0.0

New Features and Usability Improvements

  • DAOS Version 2.6 includes the production-ready version of Metadata-on-SSD (Phase1) that supports DAOS servers without Persistent Memory. In this configuration mode, application metadata is stored on SSD and cached in DRAM. It is persisted to a Write Ahead Log (WAL) on write and eventually flushed back to SSD by a background service.

  • DAOS Version 2.6 supports delayed rebuild. When delayed rebuild is set for a pool, rebuild is not triggered immediately when a failure happens. It will be started with the next pool operation from the administrator, for example pool reintegration. This can significantly reduce unnecessary data movement if the administrator can bring the failed server back within short time window (for example, when a server is rebooted).

  • DAOS pool and container services can now detect duplicated metadata RPCs. It can return the execution result from the previous RPC, instead of running the handler again which could cause nondeterministic behavior.

  • DAOS Version 2.6 supports NVMe hotplug in environments both with VMD and without VMD.

  • In DAOS 2.4 and earlier versions, the network provider specified in the server YML file is an immutable property that cannot be changed after an engine has been formatted. In DAOS Version 2.6, administrators can change the fabric provider without reformatting the system.

  • A checksum scrubber service is added to DAOS Version 2.6. It runs when the storage server is idle to limit performance impact, and it scans the object trees to verify data checksums and reports any detected errors. When a configurable threshold of checksum errors on a single pool shard is reached, the pool target will be evicted.

  • DAOS Version 2.6 now provides a production version of libpil4dfs. The libpil4dfs library intercepts I/O and metadata related functions (unlike it's counterpart libioil that intercepts only IO functions). This library provides similar performance to applications using the POSIX interface than the performance of the native DFS interface.

  • A Technology Preview of the catastrophic recovery functionality is available in DAOS Version 2.6. This feature only supports offline check and repair of DAOS system metadata in this version.

  • DAOS client side metrics is added as a Technology Preview. The daos_agent configuration file includes new parameters to control collection and export of per-client telemetry. If the telemetry_port option is set, then per-client telemetry will be published in Prometheus format for real-time sampling of client processes.

  • Flat KV objects are added in this version. This object type has only one level key in low-level data structure. This feature can reduce metadata overhead of some data models built on top of DAOS, for example POSIX files.

  • The DAOS client can query or punch large objects in collective mode, which propagagtes the RPC through a multi-level spanning tree.

  • The extent allocator of DAOS now uses a bitmap to manage small block allocation instead of always using a b+tree. This can improve allocation performance and reduce metadata overhead of the extent allocator.

  • DAOS Version 2.6 implements server side RPC throttling. This can prevent DAOS servers from running out of memory when too many clients send a high number of RPCs to the server simmultaneously.

Other notable changes

  • Removed dmg storage query device-health in favor of dmg storage list-devices --health.

  • A DAOS engine that rejoins with a different address will be rejected now. In previous versions, it was accepted but the new address was silently ignored.

  • Removed a few legacy daos_server config file syntax: scm_class and bdev_class.

  • The daos_server stand-alone commands now support JSON output (via the -j flag).

  • dmg storage query list-devices now outputs empty NSID for unplugged device.

  • Added a command line option for read-only mounting of dfuse. When set, this instructs the kernel to mount read-only.

  • Added a new scanning feature to the dfs and daos utilities to report statistics about a POSIX container.

  • Added VOS garbage collection metrics.

Known Issues and limitations

  • Some libc functions are not intercepted by pil4dfs. While most of those functions have been added, using a function that is not intercepted yet can cause a client program to crash. For the intermediate phase until all known functions are captured, we introduced an environment variable that users can set when using the pil4dfs library to get file descriptors from dfuse: Setting D_IL_COMPATIBLE=1 will enable that mode. It is expected that this mode may add a small overhead as it requires going through the fuse kernel to obtain the file descriptor.

  • High idle CPU load can occasionally happen on the DAOS engines. This is still under investigation.

  • I/O performance of certain transfer sizes may be lower than expected in some environments (combinations of Operation Systems and OFED versions). This is still under investigation.

Bug fixes

The DAOS 2.6 release includes fixes for numerous defects. For details, please refer to the Github release/2.6 commit history and the associated Jira tickets as stated in the commit messages.

Additional resources

Visit the online documentation for more information. All DAOS project source code is maintained in the https://github.com/daos-stack/daos repository. Please visit this link for more information on the DAOS license.

Refer to the System Deployment section of the DAOS Administration Guide for installation details.

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