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Analysis of caching algorithms for distributed file systems


When picking a cache replacement policy for file systems, LRU (Least Recently Used) has always been the obvious choice, because of the temporal locality found in programs and data. However, in the case of Sun NFS servers much of the locality is filtered out by the client cache. It has been conjectured that this filtering of locality by the client caches render LRU ineffective as a server cache replacement policy. This study disproves the conjecture by simulating a NFS server cache with real world traces. Traces were taken of NFS read and write requests sent to an NFS server. These traces were then run through a cache simulator using six different cache replacement policies: Least Recently Used (LRU), Least Frequently Used (LFU), Frequency Based Replacement (FBR), First In First Out (FIFO), Random (RAND), and Optimal (OPT). RAND and OPT were used to provide lower and upper bounds on performance. Results show that LRU is an effective NFS server cache replacement policy and frequency based tend to exhibit erratic behavior in the presence of temporal locality and sequentially accessed files.

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