Speaker
A. Hanushevsky
(SLAC)
Description
As the BaBar experiment shifted its computing model to a ROOT-based
framework, we undertook the development of a high-performance file server
as the basis for a fault-tolerant storage environment whose ultimate goal
was to minimize job failures due to server failures. Capitalizing on our
five years of experience with extending Objectivity's Advanced
Multithreaded Server (AMS), elements were added to remove as many
obstacles to server performance and fault-tolerance as possible. The final
outcome was xrootd, upwardly and downwardly compatible with the current
file server, rootd. This paper describes the essential protocol elements
that make high performance and fault-tolerance possible; including
asynchronous parallel requests, stream multiplexing, data pre-fetch,
automatic data segmenting, and the framework for a structured peer-to-peer
storage model that allows massive server scaling and client recovery from
multiple failures. The internal architecture of the server is also
described to explain how high performance was maintained and full
compatibility was achieved. Now in production at Stanford Linear
Accelerator Center, Rutherford Appleton Laboratory (RAL), INFN, and IN2P3;
xrootd has shown that our design provides what we set out to achieve. The
xrootd server is now part of the standard ROOT distribution so that other
experiments can benefit from this data serving model within a standard HEP
event analysis framework.
