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+# Specifying the I/O properties of a system
+
+The I/O properties of a system can be specified as a YAML string, by
+using the option --io-properties, or as a YAML file with the option
+--io-properties-file.
+
+The expected format starts with a map of sections at the top level.
+Currently only `disks` is supported.
+
+## The disks section
+
+Inside the `disks` section, the user can specify a list of mount points.
+
+For each mount point, 4 properties have to be specified (none are
+optional):
+
+* `read_iops`: read IOPS speed of the device
+* `read_bandwidth`: read bandwidth speed of the device
+* `write_iops`: write IOPS speed of the device
+* `write_bandwidth`: write bandwidth speed of the device
+
+
+Additionally the following optional properties can be added:
+
+* `read_saturation_length`: read buffer length to saturate the device throughput
+* `write_saturation_length`: write buffer length to saturate the device throughput
+
+Those quantities can be specified in raw form, or followed with a
+suffix (k, M, G, or T).
+
+Example:
+
+```
+disks:
+ - mountpoint: /var/lib/some_seastar_app
+ read_iops: 95000
+ read_bandwidth: 545M
+ write_iops: 85000
+ write_bandwidth: 510M
+ write_saturation_length: 64k
+```