Cache Faults/sec is the number of faults which occur when a page sought in the file system cache is not found there and must be retrieved from elsewhere in memory (a soft fault) or from disk (a hard fault). The file system cache is an area of physical memory that stores recently used pages of data for applications. Cache activity is a reliable indicator of most application I/O operations. This counter counts the number of faults, without regard for the number of pages faulted in each operation.