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-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 11 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
-
-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).