| =============================================== | |
| Block layer statistics in /sys/block/<dev>/stat | |
| =============================================== | |
| This file documents the contents of the /sys/block/<dev>/stat file. | |
| The stat file provides several statistics about the state of block | |
| device <dev>. | |
| Q. | |
| Why are there multiple statistics in a single file? Doesn't sysfs | |
| normally contain a single value per file? | |
| A. | |
| By having a single file, the kernel can guarantee that the statistics | |
| represent a consistent snapshot of the state of the device. If the | |
| statistics were exported as multiple files containing one statistic | |
| each, it would be impossible to guarantee that a set of readings | |
| represent a single point in time. | |
| The stat file consists of a single line of text containing 17 decimal | |
| values separated by whitespace. The fields are summarized in the | |
| following table, and described in more detail below. | |
| =============== ============= ================================================= | |
| Name units description | |
| =============== ============= ================================================= | |
| read I/Os requests number of read I/Os processed | |
| read merges requests number of read I/Os merged with in-queue I/O | |
| read sectors sectors number of sectors read | |
| read ticks milliseconds total wait time for read requests | |
| write I/Os requests number of write I/Os processed | |
| write merges requests number of write I/Os merged with in-queue I/O | |
| write sectors sectors number of sectors written | |
| write ticks milliseconds total wait time for write requests | |
| in_flight requests number of I/Os currently in flight | |
| io_ticks milliseconds total time this block device has been active | |
| time_in_queue milliseconds total wait time for all requests | |
| discard I/Os requests number of discard I/Os processed | |
| discard merges requests number of discard I/Os merged with in-queue I/O | |
| discard sectors sectors number of sectors discarded | |
| discard ticks milliseconds total wait time for discard requests | |
| flush I/Os requests number of flush I/Os processed | |
| flush ticks milliseconds total wait time for flush requests | |
| =============== ============= ================================================= | |
| read I/Os, write I/Os, discard I/0s | |
| =================================== | |
| These values increment when an I/O request completes. | |
| flush I/Os | |
| ========== | |
| These values increment when an flush I/O request completes. | |
| Block layer combines flush requests and executes at most one at a time. | |
| This counts flush requests executed by disk. Not tracked for partitions. | |
| read merges, write merges, discard merges | |
| ========================================= | |
| These values increment when an I/O request is merged with an | |
| already-queued I/O request. | |
| read sectors, write sectors, discard_sectors | |
| ============================================ | |
| These values count the number of sectors read from, written to, or | |
| discarded from this block device. The "sectors" in question are the | |
| standard UNIX 512-byte sectors, not any device- or filesystem-specific | |
| block size. The counters are incremented when the I/O completes. | |
| read ticks, write ticks, discard ticks, flush ticks | |
| =================================================== | |
| These values count the number of milliseconds that I/O requests have | |
| waited on this block device. If there are multiple I/O requests waiting, | |
| these values will increase at a rate greater than 1000/second; for | |
| example, if 60 read requests wait for an average of 30 ms, the read_ticks | |
| field will increase by 60*30 = 1800. | |
| in_flight | |
| ========= | |
| This value counts the number of I/O requests that have been issued to | |
| the device driver but have not yet completed. It does not include I/O | |
| requests that are in the queue but not yet issued to the device driver. | |
| io_ticks | |
| ======== | |
| This value counts the number of milliseconds during which the device has | |
| had I/O requests queued. | |
| time_in_queue | |
| ============= | |
| This value counts the number of milliseconds that I/O requests have waited | |
| on this block device. If there are multiple I/O requests waiting, this | |
| value will increase as the product of the number of milliseconds times the | |
| number of requests waiting (see "read ticks" above for an example). |