in_disk: add new documentation about in_disk

Signed-off-by: Takahiro YAMASHITA <[email protected]>

SUMMARY.md

@@ -20,6 +20,7 @@
     * [TLS / SSL](getting_started/tls_ssl.md)
 * [Input Plugins](input/README.md)
     * [CPU Usage](input/cpu.md)
+    * [Disk Usage](input/disk.md)
     * [Forward](input/forward.md)
     * [Head](input/head.md)
     * [Health](input/health.md)

input/README.md

@@ -5,6 +5,7 @@ The _input plugins_ defines the source from where [Fluent Bit](http://fluentbit.
 | name                        |  title             | description     |
 |-----------------------------|--------------------|-----------------|
 | [cpu](cpu.md)         | CPU Usage  | measure total CPU usage of the system.|
+| [disk](disk.md)       | Disk Usage | measure Disk I/Os. |
 | [forward](forward.md) | Forward | Fluentd forward protocol. |
 | [head](head.md)       | Head | read first part of files. |
 | [health](health.md)   | Health | Check health of TCP services. |

input/disk.md

@@ -0,0 +1,50 @@
+# Disk Usage 
+
+The __disk__ input plugin, gathers the information about the disk usage of the running system every certain interval of time and reports them.
+
+## Configuration Parameters
+
+The plugin supports the following configuration parameters:
+
+| Key           | Description |
+| --------------|-------------|
+| Interval_Sec  | Polling interval (seconds).  default: 1|
+| Interval_NSec | Polling interval (nanosecond). default: 0|
+| Dev_Name      | Device name to limit the target. (e.g. sda). If not set, _in_disk_ gathers information from all of disks and partitions.|
+
+## Getting Started
+
+In order to get disk usage from your system, you can run the plugin from the command line or through the configuration file:
+
+### Command Line
+
+```bash
+$ fluent-bit -i disk -o stdout
+Fluent-Bit v0.11.0
+Copyright (C) Treasure Data
+
+[2017/01/28 16:58:16] [ info] [engine] started
+[0] disk.0: [1485590297, {"read_size"=>0, "write_size"=>0}]
+[1] disk.0: [1485590298, {"read_size"=>0, "write_size"=>0}]
+[2] disk.0: [1485590299, {"read_size"=>0, "write_size"=>0}]
+[3] disk.0: [1485590300, {"read_size"=>0, "write_size"=>11997184}]
+```
+
+### Configuration File
+
+In your main configuration file append the following _Input_ & _Output_ sections:
+
+```python
+[INPUT]
+    Name          disk
+    Tag           disk
+    Interval_Sec  1
+    Interval_NSec 0
+[OUTPUT]
+    Name   stdout
+    Match  *
+```
+
+Note: Total interval (sec) = Interval_Sec + (Interval_Nsec / 1000000000).
+
+e.g. 1.5s = 1s + 500000000ns