Almost all data now found in RAID cache, only 15% backend disk I/O overhead

System Performance Statistics
                All Ports     Port 1     Port 2     Port 3     Port 4
  Read  MB/s:      299.1       74.0       74.7       75.1       75.2
  Write MB/s:        0.0        0.0        0.0        0.0        0.0
  Total MB/s:      299.1       74.0       74.7       75.1       75.2

  Read  IO/s:        840        209        210        211        210
  Write IO/s:          0          0          0          0          0
  Total IO/s:        836        209        210        208        209

  Read Hits:        99.5%      98.3%      99.6%     100.0%     100.0%
  Prefetch Hits:    98.8%      97.6%      98.9%      99.6%      99.0%
  Prefetches:       42.0%      41.5%      42.0%      42.9%      41.7%
  Writebacks:        0.0%       0.0%       0.0%       0.0%       0.0%
  Rebuild MB/s:      0.0        0.0        0.0        0.0        0.0
  Verify MB/s:       0.0        0.0        0.0        0.0        0.0

                    Total      Reads     Writes      Pieces   Reads     Writes
  Disk IO/s:          614        614          0        1:     39068          0
  Disk MB/s:        345.5      345.5        0.0        2:       111          0
  Disk Pieces:      39290      39290          0        3:         0          0
  BDB Pieces:                      0                   4:         0          0
                                                       5:         0          0
   Cache Writeback Data:     0.0%                      6:         0          0
   Rebuild/Verify Data:      0.0%    0.0%              7:         0          0
   Cache Data locked:        0.0%                      8:         0          0