1 ============================================== 1 ===============================================
2 Block layer statistics in /sys/block/<dev>/sta 2 Block layer statistics in /sys/block/<dev>/stat
3 ============================================== 3 ===============================================
4 4
5 This file documents the contents of the /sys/b 5 This file documents the contents of the /sys/block/<dev>/stat file.
6 6
7 The stat file provides several statistics abou 7 The stat file provides several statistics about the state of block
8 device <dev>. 8 device <dev>.
9 9
10 Q. 10 Q.
11 Why are there multiple statistics in a sing 11 Why are there multiple statistics in a single file? Doesn't sysfs
12 normally contain a single value per file? 12 normally contain a single value per file?
13 13
14 A. 14 A.
15 By having a single file, the kernel can gua 15 By having a single file, the kernel can guarantee that the statistics
16 represent a consistent snapshot of the stat 16 represent a consistent snapshot of the state of the device. If the
17 statistics were exported as multiple files 17 statistics were exported as multiple files containing one statistic
18 each, it would be impossible to guarantee t 18 each, it would be impossible to guarantee that a set of readings
19 represent a single point in time. 19 represent a single point in time.
20 20
21 The stat file consists of a single line of tex 21 The stat file consists of a single line of text containing 17 decimal
22 values separated by whitespace. The fields ar 22 values separated by whitespace. The fields are summarized in the
23 following table, and described in more detail 23 following table, and described in more detail below.
24 24
25 25
26 =============== ============= ================ 26 =============== ============= =================================================
27 Name units description 27 Name units description
28 =============== ============= ================ 28 =============== ============= =================================================
29 read I/Os requests number of read I 29 read I/Os requests number of read I/Os processed
30 read merges requests number of read I 30 read merges requests number of read I/Os merged with in-queue I/O
31 read sectors sectors number of sector 31 read sectors sectors number of sectors read
32 read ticks milliseconds total wait time 32 read ticks milliseconds total wait time for read requests
33 write I/Os requests number of write 33 write I/Os requests number of write I/Os processed
34 write merges requests number of write 34 write merges requests number of write I/Os merged with in-queue I/O
35 write sectors sectors number of sector 35 write sectors sectors number of sectors written
36 write ticks milliseconds total wait time 36 write ticks milliseconds total wait time for write requests
37 in_flight requests number of I/Os c 37 in_flight requests number of I/Os currently in flight
38 io_ticks milliseconds total time this 38 io_ticks milliseconds total time this block device has been active
39 time_in_queue milliseconds total wait time 39 time_in_queue milliseconds total wait time for all requests
40 discard I/Os requests number of discar 40 discard I/Os requests number of discard I/Os processed
41 discard merges requests number of discar 41 discard merges requests number of discard I/Os merged with in-queue I/O
42 discard sectors sectors number of sector 42 discard sectors sectors number of sectors discarded
43 discard ticks milliseconds total wait time 43 discard ticks milliseconds total wait time for discard requests
44 flush I/Os requests number of flush 44 flush I/Os requests number of flush I/Os processed
45 flush ticks milliseconds total wait time 45 flush ticks milliseconds total wait time for flush requests
46 =============== ============= ================ 46 =============== ============= =================================================
47 47
48 read I/Os, write I/Os, discard I/0s 48 read I/Os, write I/Os, discard I/0s
49 =================================== 49 ===================================
50 50
51 These values increment when an I/O request com 51 These values increment when an I/O request completes.
52 52
53 flush I/Os 53 flush I/Os
54 ========== 54 ==========
55 55
56 These values increment when an flush I/O reque 56 These values increment when an flush I/O request completes.
57 57
58 Block layer combines flush requests and execut 58 Block layer combines flush requests and executes at most one at a time.
59 This counts flush requests executed by disk. N 59 This counts flush requests executed by disk. Not tracked for partitions.
60 60
61 read merges, write merges, discard merges 61 read merges, write merges, discard merges
62 ========================================= 62 =========================================
63 63
64 These values increment when an I/O request is 64 These values increment when an I/O request is merged with an
65 already-queued I/O request. 65 already-queued I/O request.
66 66
67 read sectors, write sectors, discard_sectors 67 read sectors, write sectors, discard_sectors
68 ============================================ 68 ============================================
69 69
70 These values count the number of sectors read 70 These values count the number of sectors read from, written to, or
71 discarded from this block device. The "sector 71 discarded from this block device. The "sectors" in question are the
72 standard UNIX 512-byte sectors, not any device 72 standard UNIX 512-byte sectors, not any device- or filesystem-specific
73 block size. The counters are incremented when 73 block size. The counters are incremented when the I/O completes.
74 74
75 read ticks, write ticks, discard ticks, flush 75 read ticks, write ticks, discard ticks, flush ticks
76 ============================================== 76 ===================================================
77 77
78 These values count the number of milliseconds 78 These values count the number of milliseconds that I/O requests have
79 waited on this block device. If there are mul 79 waited on this block device. If there are multiple I/O requests waiting,
80 these values will increase at a rate greater t 80 these values will increase at a rate greater than 1000/second; for
81 example, if 60 read requests wait for an avera 81 example, if 60 read requests wait for an average of 30 ms, the read_ticks
82 field will increase by 60*30 = 1800. 82 field will increase by 60*30 = 1800.
83 83
84 in_flight 84 in_flight
85 ========= 85 =========
86 86
87 This value counts the number of I/O requests t 87 This value counts the number of I/O requests that have been issued to
88 the device driver but have not yet completed. 88 the device driver but have not yet completed. It does not include I/O
89 requests that are in the queue but not yet iss 89 requests that are in the queue but not yet issued to the device driver.
90 90
91 io_ticks 91 io_ticks
92 ======== 92 ========
93 93
94 This value counts the number of milliseconds d 94 This value counts the number of milliseconds during which the device has
95 had I/O requests queued. 95 had I/O requests queued.
96 96
97 time_in_queue 97 time_in_queue
98 ============= 98 =============
99 99
100 This value counts the number of milliseconds t 100 This value counts the number of milliseconds that I/O requests have waited
101 on this block device. If there are multiple I 101 on this block device. If there are multiple I/O requests waiting, this
102 value will increase as the product of the numb 102 value will increase as the product of the number of milliseconds times the
103 number of requests waiting (see "read ticks" a 103 number of requests waiting (see "read ticks" above for an example).
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