1 ==============================================
2 Block layer statistics in /sys/block/<dev>/sta
3 ==============================================
4
5 This file documents the contents of the /sys/b
6
7 The stat file provides several statistics abou
8 device <dev>.
9
10 Q.
11 Why are there multiple statistics in a sing
12 normally contain a single value per file?
13
14 A.
15 By having a single file, the kernel can gua
16 represent a consistent snapshot of the stat
17 statistics were exported as multiple files
18 each, it would be impossible to guarantee t
19 represent a single point in time.
20
21 The stat file consists of a single line of tex
22 values separated by whitespace. The fields ar
23 following table, and described in more detail
24
25
26 =============== ============= ================
27 Name units description
28 =============== ============= ================
29 read I/Os requests number of read I
30 read merges requests number of read I
31 read sectors sectors number of sector
32 read ticks milliseconds total wait time
33 write I/Os requests number of write
34 write merges requests number of write
35 write sectors sectors number of sector
36 write ticks milliseconds total wait time
37 in_flight requests number of I/Os c
38 io_ticks milliseconds total time this
39 time_in_queue milliseconds total wait time
40 discard I/Os requests number of discar
41 discard merges requests number of discar
42 discard sectors sectors number of sector
43 discard ticks milliseconds total wait time
44 flush I/Os requests number of flush
45 flush ticks milliseconds total wait time
46 =============== ============= ================
47
48 read I/Os, write I/Os, discard I/0s
49 ===================================
50
51 These values increment when an I/O request com
52
53 flush I/Os
54 ==========
55
56 These values increment when an flush I/O reque
57
58 Block layer combines flush requests and execut
59 This counts flush requests executed by disk. N
60
61 read merges, write merges, discard merges
62 =========================================
63
64 These values increment when an I/O request is
65 already-queued I/O request.
66
67 read sectors, write sectors, discard_sectors
68 ============================================
69
70 These values count the number of sectors read
71 discarded from this block device. The "sector
72 standard UNIX 512-byte sectors, not any device
73 block size. The counters are incremented when
74
75 read ticks, write ticks, discard ticks, flush
76 ==============================================
77
78 These values count the number of milliseconds
79 waited on this block device. If there are mul
80 these values will increase at a rate greater t
81 example, if 60 read requests wait for an avera
82 field will increase by 60*30 = 1800.
83
84 in_flight
85 =========
86
87 This value counts the number of I/O requests t
88 the device driver but have not yet completed.
89 requests that are in the queue but not yet iss
90
91 io_ticks
92 ========
93
94 This value counts the number of milliseconds d
95 had I/O requests queued.
96
97 time_in_queue
98 =============
99
100 This value counts the number of milliseconds t
101 on this block device. If there are multiple I
102 value will increase as the product of the numb
103 number of requests waiting (see "read ticks" a
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