Based on kernel version 3.9. Page generated on 2013-05-02 22:55 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).