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