1 The following are demonstrations of the rfsio.d script. 2 3 4 5 Here we trace file read() activity that has fully missed the cache and 6 must be read from disk, 7 8 # ./rfsio.d 9 10 Read IOPS (count) 11 / logical 7 12 /extra1 physical 162 13 /boot logical 235 14 /boot physical 410 15 /extra1 logical 9514 16 17 Read Bandwidth (bytes) 18 / logical 533 19 /boot logical 1502386 20 /boot physical 1512960 21 /extra1 physical 97153024 22 /extra1 logical 97228668 23 24 Total File System miss-rate: 100% 25 ^C 26 27 The miss rate of 100% means that all of the file system activity missed 28 the cache, and had to read from disk. 29 30 31 32 The following demonstrates file read() activity to the root filesystem 33 that mostly returned from the file system cache. 34 35 # ./rfsio.d 36 37 Read IOPS (count) 38 / physical 1 39 /extra1 physical 9 40 /devices logical 9 41 / logical 15 42 /extra1 logical 4096 43 44 Read Bandwidth (bytes) 45 /devices logical 9 46 / logical 949 47 / physical 8192 48 /extra1 physical 917504 49 /extra1 logical 4194304 50 51 Total File System miss-rate: 22% 52 ^C 53 54 The total miss-rate was 22%, which is based on the bytes transferred that 55 missed the cache. 56 57 58 59 60 Now for an unusual demonstration, 61 62 # ./rfsio.d 63 64 Read IOPS (count) 65 /devices logical 1 66 / logical 10 67 /extra1 physical 106 68 /extra1 logical 6337 69 70 Read Bandwidth (bytes) 71 /devices logical 2 72 / logical 961 73 /extra1 logical 64846450 74 /extra1 physical 66151424 75 76 Total File System miss-rate: 102% 77 ^C 78 79 Here the miss-rate is 102%, which indicates that more data was read from 80 disk than was requested; this can occur due to UFS read-ahead, which 81 assists the performance of sequential disk activity at the small risk of 82 reading too much data. 83
Indexes created Fri Apr 24 00:22:58 UTC 2026