Block layer statistics in /sys/block/<dev>/stat — The Linux Kernel 5.18.5-gnu-1 documentation

# 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>.

17. Why are there multiple statistics in a single file? Doesn’t sysfs normally contain a single value per file?

1. 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).