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File System Access (XRootd)

File System Access (XRootd). Andrew Hanushevsky Stanford Linear Accelerator Center 13-Jan-03. Goals. High Performance File-Based Access Scalable Extensible Mass Storage integration Flexible Security Dynamically Configurable Rootd Compatable. Achieving High Performance.

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File System Access (XRootd)

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  1. File System Access(XRootd) Andrew Hanushevsky Stanford Linear Accelerator Center 13-Jan-03

  2. Goals • High Performance File-Based Access • Scalable • Extensible • Mass Storage integration • Flexible Security • Dynamically Configurable • Rootd Compatable 2: XRootd

  3. Achieving High Performance • Multi-threaded server • Ability to run multiple servers on one host • MRU polling • Last active connections serviced first • Sticky sockets • Socket/thread bound for “active” connections • Using high-performance oofs layer • Unlocked I/O, sync reduction, file descriptor partitioning 3: XRootd

  4. Achieving Scalability • Socket multiplexing • One connection per client/host • Requires stream id protocol extensions • Dynamic Load Balancing • Requires client redirection protocol extensions • Using scalable oofs layer • File reuse, idle closeouts, cached file system 4: XRootd

  5. Achieving Extensibility • Opaque Information Protocol • Protocol extension allows client to relay outboard information to server • Messaging interface • Cache group • Request priority • Other things we haven’t thought of yet… 5: XRootd

  6. Achieving MSS Integration • Using oofs layer • Already integrates with almost any MSS • No brainer 6: XRootd

  7. Achieving Flexible Security • Negotiated Security Protocol Extensions • Allows client/server to agree on protocol • E.g., Kerberos, GSI, AFS Kerberos, etc. • Using oofs layer • Multi-protocol authentication support • Scalable authorization 7: XRootd

  8. Achieving Configurability • Servers must come up/down without harm • Part of dynamic load balancing • Requires client retry extension 8: XRootd

  9. Achieving Compatability • Client sensitive to server version number • Rootd servers default to base TNetFile class • XRootd servers use derived TNetFile class • Server requires client to turn on extensions • Base TNetFile class restricted to rootd ops • Derived TNetFile enables extensions • Multi-streaming, Redirection, Request Deferral, Generic Security, Opaque Information 9: XRootd

  10. security xrootd Architecture application Database Protocol Layer xrootd Filesystem Logical Layer oofs Filesystem Physical Layer ooss Filesystem Implementation xfs mss 10: XRootd

  11. Some Details • Compatible Protocol • Allows transparent use of rootd & xrootd • Multi-Streaming • Allows multiple files per connection • Cache File System • Dynamic Load Balancing • Client directed to “appropriate” server • Configurability & Recoverability 11: XRootd

  12. Compatible Protocol Application xrootd XTNetFile xrootd rootd compability TNetFile rootd 12: XRootd

  13. Multi-Streaming • Each open() assigned a stream number • Four character id that starts with 0-9 • All requests/responses identify relevant stream • Non-open file requests use arbitrary id • Any four characters not starting with 0-9 • E.g., stat(), mv(), unlink(), etc. • Parallel Multi-Streaming allowed • Client must explicitly enable it 13: XRootd

  14. Cache File System Index Area Optional data cache Default data area /databases/mydbfile symlink Naming convention allows for audit and index recovery Multiple Independent Filesystems /cache1/databases:mydbfile Data Area Any number Any Size Chosen based on free space in LRU order /cache2 /cache3 14: XRootd

  15. ufs ufs ufs Dynamic Load Balancing xrootd Dynamic Selection xrootd mss client xrootd 15: XRootd

  16. xrootd xrootd xrootd (any number) dlbd dlbd dlbd dlbd (any number) xrootd DLB Implementation I do subscribe who has the file? open again open Client wait try host:port 16: XRootd

  17. Configurability & Recoverability • Go hand in hand • Configuration changes may be disruptive • Must be able to recover from dynamic configuration changes • Dynamic Load Balancing essential part 17: XRootd

  18. Recoverability • Whenever client looses r/o connection • Back to distinguished xrootd(s) for reselection • Whenever client looses r/w connection • Limited wait/retry loop on the same server • We will be working to improve this next year! • All handled in the XTNetFile class • Disruptions merely delay the client 18: XRootd

  19. Configurability • Since we have recoverability… • Servers may come and go • New servers can be added at any time • Servers may be brought down for maintenance • Files can be moved around in real-time • Client will recover and adjust to the new configuration 19: XRootd

  20. Conclusion • Goals for rootd file access can be met • Most of this work relies on leveraging work done for the AMS • Compatability allows us to lobby the community for xrootd to become the default “rootd” 20: XRootd

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