# DiskIO Input Plugin

The diskio input plugin gathers metrics about disk traffic and timing.

## Configuration

```toml
# Read metrics about disk IO by device
[[inputs.diskio]]
  ## By default, telegraf will gather stats for all devices including
  ## disk partitions.
  ## Setting devices will restrict the stats to the specified devices.
  # devices = ["sda", "sdb"]
  ## Uncomment the following line if you need disk serial numbers.
  # skip_serial_number = false
  #
  ## On systems which support it, device metadata can be added in the form of
  ## tags.
  ## Currently only Linux is supported via udev properties. You can view
  ## available properties for a device by running:
  ## 'udevadm info -q property -n /dev/sda'
  ## Note: Most, but not all, udev properties can be accessed this way. Properties
  ## that are currently inaccessible include DEVTYPE, DEVNAME, and DEVPATH.
  # device_tags = ["ID_FS_TYPE", "ID_FS_USAGE"]
  #
  ## Using the same metadata source as device_tags, you can also customize the
  ## name of the device via templates.
  ## The 'name_templates' parameter is a list of templates to try and apply to
  ## the device. The template may contain variables in the form of '$PROPERTY' or
  ## '${PROPERTY}'. The first template which does not contain any variables not
  ## present for the device is used as the device name tag.
  ## The typical use case is for LVM volumes, to get the VG/LV name instead of
  ## the near-meaningless DM-0 name.
  # name_templates = ["$ID_FS_LABEL","$DM_VG_NAME/$DM_LV_NAME"]
```

### Docker container

To monitor the Docker engine host from within a container you will need to
mount the host's filesystem into the container and set the `HOST_PROC`
environment variable to the location of the `/proc` filesystem.  Additionally,
it is required to use privileged mode to provide access to `/dev`.

If you are using the `device_tags` or `name_templates` options, you will need
to bind mount `/run/udev` into the container.

```shell
docker run --privileged -v /:/hostfs:ro -v /run/udev:/run/udev:ro -e HOST_PROC=/hostfs/proc telegraf
```

## Metrics

- diskio
  - tags:
    - name (device name)
    - serial (device serial number)
  - fields:
    - reads (integer, counter)
    - writes (integer, counter)
    - read_bytes (integer, counter, bytes)
    - write_bytes (integer, counter, bytes)
    - read_time (integer, counter, milliseconds)
    - write_time (integer, counter, milliseconds)
    - io_time (integer, counter, milliseconds)
    - weighted_io_time (integer, counter, milliseconds)
    - iops_in_progress (integer, gauge)
    - merged_reads (integer, counter)
    - merged_writes (integer, counter)

On linux these values correspond to the values in
[`/proc/diskstats`](https://www.kernel.org/doc/Documentation/ABI/testing/procfs-diskstats)
and
[`/sys/block/<dev>/stat`](https://www.kernel.org/doc/Documentation/block/stat.txt).

### `reads` & `writes`

These values increment when an I/O request completes.

### `read_bytes` & `write_bytes`

These values count the number of bytes read from or written to this
block device.

### `read_time` & `write_time`

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_time
field will increase by 60*30 = 1800.

### `io_time`

This value counts the number of milliseconds during which the device has
had I/O requests queued.

### `weighted_io_time`

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_time` above for an example).

### `iops_in_progress`

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.

### `merged_reads` & `merged_writes`

Reads and writes which are adjacent to each other may be merged for
efficiency.  Thus two 4K reads may become one 8K read before it is
ultimately handed to the disk, and so it will be counted (and queued)
as only one I/O. These fields lets you know how often this was done.

## Sample Queries

### Calculate percent IO utilization per disk and host

```sql
SELECT non_negative_derivative(last("io_time"),1ms) FROM "diskio" WHERE time > now() - 30m GROUP BY "host","name",time(60s)
```

### Calculate average queue depth

`iops_in_progress` will give you an instantaneous value. This will give you the average between polling intervals.

```sql
SELECT non_negative_derivative(last("weighted_io_time"),1ms) from "diskio" WHERE time > now() - 30m GROUP BY "host","name",time(60s)
```

## Example

```shell
diskio,name=sda1 merged_reads=0i,reads=2353i,writes=10i,write_bytes=2117632i,write_time=49i,io_time=1271i,weighted_io_time=1350i,read_bytes=31350272i,read_time=1303i,iops_in_progress=0i,merged_writes=0i 1578326400000000000
diskio,name=centos/var_log reads=1063077i,writes=591025i,read_bytes=139325491712i,write_bytes=144233131520i,read_time=650221i,write_time=24368817i,io_time=852490i,weighted_io_time=25037394i,iops_in_progress=1i,merged_reads=0i,merged_writes=0i 1578326400000000000
diskio,name=sda write_time=49i,io_time=1317i,weighted_io_time=1404i,reads=2495i,read_time=1357i,write_bytes=2117632i,iops_in_progress=0i,merged_reads=0i,merged_writes=0i,writes=10i,read_bytes=38956544i 1578326400000000000
```
