| =============================================== |
| 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). |
