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+Device Management
+=================
+
+Ceph tracks which hardware storage devices (e.g., HDDs, SSDs) are consumed by
+which daemons, and collects health metrics about those devices in order to
+provide tools to predict and/or automatically respond to hardware failure.
+
+Device tracking
+---------------
+
+You can query which storage devices are in use with::
+
+  ceph device ls
+
+You can also list devices by daemon or by host::
+
+  ceph device ls-by-daemon <daemon>
+  ceph device ls-by-host <host>
+
+For any individual device, you can query information about its
+location and how it is being consumed with::
+
+  ceph device info <devid>
+
+
+Enabling monitoring
+-------------------
+
+Ceph can also monitor health metrics associated with your device.  For
+example, SATA hard disks implement a standard called SMART that
+provides a wide range of internal metrics about the device's usage and
+health, like the number of hours powered on, number of power cycles,
+or unrecoverable read errors.  Other device types like SAS and NVMe
+implement a similar set of metrics (via slightly different standards).
+All of these can be collected by Ceph via the ``smartctl`` tool.
+
+You can enable or disable health monitoring with::
+
+  ceph device monitoring on
+
+or::
+
+  ceph device monitoring off
+
+
+Scraping
+--------
+
+If monitoring is enabled, metrics will automatically be scraped at regular intervals.  That interval can be configured with::
+
+  ceph config set mgr mgr/devicehealth/scrape_frequency <seconds>
+
+The default is to scrape once every 24 hours.
+
+You can manually trigger a scrape of all devices with::
+
+  ceph device scrape-health-metrics
+
+A single device can be scraped with::
+
+  ceph device scrape-health-metrics <device-id>
+
+Or a single daemon's devices can be scraped with::
+
+  ceph device scrape-daemon-health-metrics <who>
+
+The stored health metrics for a device can be retrieved (optionally
+for a specific timestamp) with::
+
+  ceph device get-health-metrics <devid> [sample-timestamp]
+
+Failure prediction
+------------------
+
+Ceph can predict life expectancy and device failures based on the
+health metrics it collects.  There are three modes:
+
+* *none*: disable device failure prediction.
+* *local*: use a pre-trained prediction model from the ceph-mgr daemon
+* *cloud*: share device health and performance metrics an external
+  cloud service run by ProphetStor, using either their free service or
+  a paid service with more accurate predictions
+
+The prediction mode can be configured with::
+
+  ceph config set global device_failure_prediction_mode <mode>
+
+Prediction normally runs in the background on a periodic basis, so it
+may take some time before life expectancy values are populated.  You
+can see the life expectancy of all devices in output from::
+
+  ceph device ls
+
+You can also query the metadata for a specific device with::
+
+  ceph device info <devid>
+
+You can explicitly force prediction of a device's life expectancy with::
+
+  ceph device predict-life-expectancy <devid>
+
+If you are not using Ceph's internal device failure prediction but
+have some external source of information about device failures, you
+can inform Ceph of a device's life expectancy with::
+
+  ceph device set-life-expectancy <devid> <from> [<to>]
+
+Life expectancies are expressed as a time interval so that
+uncertainty can be expressed in the form of a wide interval. The
+interval end can also be left unspecified.
+
+Health alerts
+-------------
+
+The ``mgr/devicehealth/warn_threshold`` controls how soon an expected
+device failure must be before we generate a health warning.
+
+The stored life expectancy of all devices can be checked, and any
+appropriate health alerts generated, with::
+
+  ceph device check-health
+
+Automatic Mitigation
+--------------------
+
+If the ``mgr/devicehealth/self_heal`` option is enabled (it is by
+default), then for devices that are expected to fail soon the module
+will automatically migrate data away from them by marking the devices
+"out".
+
+The ``mgr/devicehealth/mark_out_threshold`` controls how soon an
+expected device failure must be before we automatically mark an osd
+"out".