HEPunion filesystem implementation as Linux module

by SAKET for CERN SFT

At CERN LHCb experiment (Large Hadron Collider beauty), in order to reconstitute and filter events, a huge computing facility is required (currently ~1500 nodes). This computing farm, runs SLC (Scientific Linux CERN), a Red Hat Enterprise Linux (RHEL) derivate. All these computing nodes get their operating system (Linux) from some dedicated servers. Each node act as diskless nodes and use dhcp and pxe/NetBoot images, loads the kernel and initial ram disk with tftp and finally loads the rest of the system from nfs which makes booting very fast.To add flexibility to the diskless nodes handling, file system union has to be added, which is often implemented in Linux live media. The aim of this project is to adapt and extend union file system as a proper Linux module to address the requirements of a HEP experiment's dedicated farm.