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Based on kernel version 3.16. Page generated on 2014-08-06 21:36 EST.

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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