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  1. assembly/
  2. bin/
  3. client/
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  5. doc/
  6. docker/
  7. hdfs/
  8. libexec/
  9. namenode/
  10. rpc/
  11. rpc-darpc/
  12. rpc-narpc/
  13. storage/
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  16. storage-rdma/
  17. .gitignore
  18. checkstyle.xml
  21. HISTORY.md
  23. NOTICE
  24. pom.xml
  25. README.md

license Documentation Status

Apache Crail (incubating)

Apache Crail is a fast multi-tiered distributed storage system designed from ground up for high-performance network and storage hardware. It marks the backbone of the Crail I/O architecture, which is described in more detail on crail.incubator.apache.org. The unique features of Crail include:

  • Zero-copy network access from userspace
  • Integration of multiple storage tiers such DRAM, flash and disaggregated shared storage
  • Ultra-low latencies for both meta data and data operations. For instance: opening, reading and closing a small file residing in the distributed DRAM tier less than 10 microseconds, which is in the same ballpark as some of the fastest RDMA-based key/value stores
  • High-performance sequential read/write operations: For instance: read operations on large files residing in the distributed DRAM tier are typically limited only by the performance of the network
  • Very low CPU consumption: a single core sharing both application and file system client can drive sequential read/write operations at the speed of up to 100Gbps and more
  • Asynchronous API leveraging the asynchronous nature of RDMA-based networking hardware
  • Extensible plugin architecture: new storage tiers tailored to specific hardware can be added easily

Crail is implemented in Java offering a Java API which integrates directly with the Java off-heap memory. Crail is designed for performance critical temporary data within a scope of a rack or two.


The documentation can be accessed by running make html in /doc and opening /doc/build/html/index.html for information about how to deploy, run, test and program against Crail. The latest version of the documentation can be found at https://incubator-crail.readthedocs.org.


Please join the Crail developer mailing list for discussions and notifications. The list is at:



Apache Crail is an effort undergoing incubation at The Apache Software Foundation (ASF), sponsored by the Apache Incubator PMC. Incubation is required of all newly accepted projects until a further review indicates that the infrastructure, communications, and decision making process have stabilized in a manner consistent with other successful ASF projects. While incubation status is not necessarily a reflection of the completeness or stability of the code, it does indicate that the project has yet to be fully endorsed by the ASF.