We present part of our recent work on performance enhancement of cluster file systems using shared disks over a SAN. This work is built around the proposal of pCFS, a file system specifically targeting those environments. In we presented the objectives and design principles of pCFS and a proof-of-concept implementation, carried out by modifying Red Hatpsilas GFS , showing significant improvements in operations over files shared among processes running in different nodes. pCFS differs from GFS in two main aspects: its use of cooperative caching and a finer grain of locking. The first aspect, which used the LAN to enhance performance in write sharing situations, was described elsewhere ; we now introduce a complementary strategy - locking file regions instead of the whole file - which enables us to use the SAN while delivering a high level of performance in those same write sharing situations. pCFS may apply inter-node locks to regions, allowing processes to operate in parallel with a minimum of coherency overhead among nodes; a process cannot access outside its region(s) and, when a writer unlocks a region, others can then lock it and be able to see modified data immediately. Through a set of experiments where a file is shared between processes running in different nodes, we show that the described approach allows a gain of, at least, an order of magnitude over plain GFS.

This short paper describes the cooperative caching architecture of pCFS, a shared disk cluster file system (CFS) which aims to achieve high performance in a broad spectrum of I/O intensive applications ranging from computational access to large data sets to video streaming and databases, and includes an extended API for parallel I/O access. pCFS is targeted at small to medium sized clusters where data is stored in fibre channel shared devices on a storage area network (SAN) and exploits two interconnect fabrics: a SAN to access on-disk data, and a LAN, used both for the exchange of control information (related to locking and cache management) and for cooperative caching dataflow