Version 17 (modified by omsynge, 15 years ago) (diff)


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.

Last Modified Wed Oct 5 14:23:21 2022 by Martin Radicke