The xrootd implementation in dCache

Starting from Version 1.7.0, dCache ships with its own implementation of the xroot file transfer protocol as a native dCache component. It acts as a fully functional xrootd server, which works against the well-known and already deployed xrootd clients. In fact xrootd/dCache works as you would expect from the native ​SLAC xrootd server daemon, letting analysis jobs transparently access files from the dCache storage element using the xroot protocol.

The Details

• dCache serves as an SRM-managed Storage Element (SE) as defined in the LCG Grid context, which means
  • We support the SRM 1.1 and with dCache 1.8 the SRM 2.2 interface definition.
  • We provide the gsiFtp wide area transfer protocol.
  • We provide local area (posix like) protocols like dCap and xRoot.
  • We publish information based on the define Glue schema.
• having all this provided by a single SE significantly reduces the administration overhead
• The xRoot protocol implementation in dCache makes full usage of dCache's core functionality, e.g.:
  • load balancing
  • file replication on heavy load
  • file migration to/from a tape backend (if present)
• xRoot requests to dCache may be handled exactly as requests made by other dCache supported protocols (dCap, GridFTP) or seperate rules may be applied, e.g.
  • pools may be shared among protocols or a set of pools may be dedicated to the xRoot protocol only.
  • special queues may be setup on pool nodes in order to balance xRoot access against accesses by other protocols, as this is already commonly uses for gsiFtp and dCap.
• security for xrootd/dCache
  • read-only access by default
  • restricted write access to protect other VOs/parts of the storage instance
  • token-based authorization (Alice security model)
  • as soon as the dCache team has a clear understanding how the xRoot security model of the (non-alice) experiments look like, the xRoot implementation in dCache will support gPlazma, the generic dCache Authorization module.
• works against standard xrootd clients: xrdcp command line client to copy whole files in and out, remote random file access from within the ROOT analysis framework

Further information

A good overview about xrootd/dCache can be found ​here. For further documentation on how to configure the xRoot protocol functionality in dCache, please consult ​dCache book.

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Last Modified Sat May 21 14:09:48 2022 by Martin Radicke