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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).
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