Sync Fast Reads/sec is the frequency of reads from the file system cache that bypass the installed file system and retrieve ...

Sync Fast Reads/sec is the frequency of reads from the file system cache that bypass the installed file system and retrieve the data directly from the cache.  Normally, file I/O requests invoke the appropriate file system to retrieve data from a file, but this path permits direct retrieval of data from the cache without file system involvement if the data is in the cache.  Even if the data is not in the cache, one invocation of the file system is avoided.  If the data is not in the cache, the request (application program call) will wait until the data has been retrieved from disk.