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stat.txt

Guest on 10th August 2021 05:09:59 PM

  1. Block layer statistics in /sys/block/<dev>/stat
  2. ===============================================
  3.  
  4. This file documents the contents of the /sys/block/<dev>/stat file.
  5.  
  6. The stat file provides several statistics about the state of block
  7. device <dev>.
  8.  
  9. Q. Why are there multiple statistics in a single file?  Doesn't sysfs
  10.    normally contain a single value per file?
  11. A. By having a single file, the kernel can guarantee that the statistics
  12.    represent a consistent snapshot of the state of the device.  If the
  13.    statistics were exported as multiple files containing one statistic
  14.    each, it would be impossible to guarantee that a set of readings
  15.    represent a single point in time.
  16.  
  17. The stat file consists of a single line of text containing 11 decimal
  18. values separated by whitespace.  The fields are summarized in the
  19. following table, and described in more detail below.
  20.  
  21. Name            units         description
  22. ----            -----         -----------
  23. read I/Os       requests      number of read I/Os processed
  24. read merges     requests      number of read I/Os merged with in-queue I/O
  25. read sectors    sectors       number of sectors read
  26. read ticks      milliseconds  total wait time for read requests
  27. write I/Os      requests      number of write I/Os processed
  28. write merges    requests      number of write I/Os merged with in-queue I/O
  29. write sectors   sectors       number of sectors written
  30. write ticks     milliseconds  total wait time for write requests
  31. in_flight       requests      number of I/Os currently in flight
  32. io_ticks        milliseconds  total time this block device has been active
  33. time_in_queue   milliseconds  total wait time for all requests
  34.  
  35. read I/Os, write I/Os
  36. =====================
  37.  
  38. These values increment when an I/O request completes.
  39.  
  40. read merges, write merges
  41. =========================
  42.  
  43. These values increment when an I/O request is merged with an
  44. already-queued I/O request.
  45.  
  46. read sectors, write sectors
  47. ===========================
  48.  
  49. These values count the number of sectors read from or written to this
  50. block device.  The "sectors" in question are the standard UNIX 512-byte
  51. sectors, not any device- or filesystem-specific block size.  The
  52. counters are incremented when the I/O completes.
  53.  
  54. read ticks, write ticks
  55. =======================
  56.  
  57. These values count the number of milliseconds that I/O requests have
  58. waited on this block device.  If there are multiple I/O requests waiting,
  59. these values will increase at a rate greater than 1000/second; for
  60. example, if 60 read requests wait for an average of 30 ms, the read_ticks
  61. field will increase by 60*30 = 1800.
  62.  
  63. in_flight
  64. =========
  65.  
  66. This value counts the number of I/O requests that have been issued to
  67. the device driver but have not yet completed.  It does not include I/O
  68. requests that are in the queue but not yet issued to the device driver.
  69.  
  70. io_ticks
  71. ========
  72.  
  73. This value counts the number of milliseconds during which the device has
  74. had I/O requests queued.
  75.  
  76. time_in_queue
  77. =============
  78.  
  79. This value counts the number of milliseconds that I/O requests have waited
  80. on this block device.  If there are multiple I/O requests waiting, this
  81. value will increase as the product of the number of milliseconds times the
  82. number of requests waiting (see "read ticks" above for an example).

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