block device 의 stat 정보 해석하기

cat /sys/block/<dev>/stat 의 정보

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

read I/Os, write I/Os
=====================

These values increment when an I/O request completes.

read merges, write merges
=========================

These values increment when an I/O request is merged with an
already-queued I/O request.

read sectors, write sectors
===========================

These values count the number of sectors read from or written to 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
=======================

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).