The algorithms around the ZFS Arc are one of the best at all. If you want to increase hit rate, you can add more RAM or add an L2Arc SSD (not as fast)
Not sure if this is good or bad. I had some huge directories from a recovered disk, not sure how having many files on the file system can affect the cache (if they should be moved to an area that has cache disabled since they are really just sitting there waiting for me to sort them).
Pretty much what I am seeing:
time hit% dh% ph% mh% arcsz 05:59:46 40 39 100 38 5.8G 05:59:56 38 37 100 38 5.8G 06:00:06 64 64 83 55 5.8G System Memory: Physical RAM: 32759 MB Free Memory : 25227 MB LotsFree: 511 MB ZFS Tunables (/etc/system): ARC Size: Current Size: 5952 MB (arcsize) Target Size (Adaptive): 31479 MB (c) Min Size (Hard Limit): 3934 MB (zfs_arc_min) Max Size (Hard Limit): 31479 MB (zfs_arc_max) ARC Size Breakdown: Most Recently Used Cache Size: 50% 15739 MB (p) Most Frequently Used Cache Size: 50% 15739 MB (c-p) ARC Efficency: Cache Access Total: 450271 Cache Hit Ratio: 76% 345448 [Defined State for buffer] Cache Miss Ratio: 23% 104823 [Undefined State for Buffer] REAL Hit Ratio: 63% 286969 [MRU/MFU Hits Only] Data Demand Efficiency: 92% Data Prefetch Efficiency: 62% CACHE HITS BY CACHE LIST: Anon: 16% 58479 [ New Customer, First Cache Hit ] Most Recently Used: 26% 90886 (mru) [ Return Customer ] Most Frequently Used: 56% 196083 (mfu) [ Frequent Customer ] Most Recently Used Ghost: 0% 0 (mru_ghost) [ Return Customer Evicted, Now Back ] Most Frequently Used Ghost: 0% 0 (mfu_ghost) [ Frequent Customer Evicted, Now Back ] CACHE HITS BY DATA TYPE: Demand Data: 62% 214687 Prefetch Data: 15% 54874 Demand Metadata: 20% 72282 Prefetch Metadata: 1% 3605 CACHE MISSES BY DATA TYPE: Demand Data: 16% 17125 Prefetch Data: 31% 32728 Demand Metadata: 50% 53419 Prefetch Metadata: 1% 1551