cddl/contrib/dtracetoolkit/Examples/rfsio_example.txt

   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.