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+.. _ceph-volume-simple-scan:
+
+``scan``
+========
+Scanning allows to capture any important details from an already-deployed OSD
+so that ``ceph-volume`` can manage it without the need of any other startup
+workflows or tools (like ``udev`` or ``ceph-disk``). Encryption with LUKS or
+PLAIN formats is fully supported.
+
+The command has the ability to inspect a running OSD, by inspecting the
+directory where the OSD data is stored, or by consuming the data partition.
+The command can also scan all running OSDs if no path or device is provided.
+
+Once scanned, information will (by default) persist the metadata as JSON in
+a file in ``/etc/ceph/osd``. This ``JSON`` file will use the naming convention
+of: ``{OSD ID}-{OSD FSID}.json``. An OSD with an id of 1, and an FSID like
+``86ebd829-1405-43d3-8fd6-4cbc9b6ecf96`` the absolute path of the file would
+be::
+
+    /etc/ceph/osd/1-86ebd829-1405-43d3-8fd6-4cbc9b6ecf96.json
+
+The ``scan`` subcommand will refuse to write to this file if it already exists.
+If overwriting the contents is needed, the ``--force`` flag must be used::
+
+    ceph-volume simple scan --force {path}
+
+If there is no need to persist the ``JSON`` metadata, there is support to send
+the contents to ``stdout`` (no file will be written)::
+
+    ceph-volume simple scan --stdout {path}
+
+
+.. _ceph-volume-simple-scan-directory:
+
+Running OSDs scan
+-----------------
+Using this command without providing an OSD directory or device will scan the
+directories of any currently running OSDs. If a running OSD was not created
+by ceph-disk it will be ignored and not scanned.
+
+To scan all running ceph-disk OSDs, the command would look like::
+
+    ceph-volume simple scan
+
+Directory scan
+--------------
+The directory scan will capture OSD file contents from interesting files. There
+are a few files that must exist in order to have a successful scan:
+
+* ``ceph_fsid``
+* ``fsid``
+* ``keyring``
+* ``ready``
+* ``type``
+* ``whoami``
+
+If the OSD is encrypted, it will additionally add the following keys:
+
+* ``encrypted``
+* ``encryption_type``
+* ``lockbox_keyring``
+
+In the case of any other file, as long as it is not a binary or a directory, it
+will also get captured and persisted as part of the JSON object.
+
+The convention for the keys in the JSON object is that any file name will be
+a key, and its contents will be its value. If the contents are a single line
+(like in the case of the ``whoami``) the contents are trimmed, and the newline
+is dropped. For example with an OSD with an id of 1, this is how the JSON entry
+would look like::
+
+    "whoami": "1",
+
+For files that may have more than one line, the contents are left as-is, except
+for keyrings which are treated specially and parsed to extract the keyring. For
+example, a ``keyring`` that gets read as::
+
+    [osd.1]\n\tkey = AQBBJ/dZp57NIBAAtnuQS9WOS0hnLVe0rZnE6Q==\n
+
+Would get stored as::
+
+    "keyring": "AQBBJ/dZp57NIBAAtnuQS9WOS0hnLVe0rZnE6Q==",
+
+
+For a directory like ``/var/lib/ceph/osd/ceph-1``, the command could look
+like::
+
+    ceph-volume simple scan /var/lib/ceph/osd/ceph1
+
+
+.. _ceph-volume-simple-scan-device:
+
+Device scan
+-----------
+When an OSD directory is not available (OSD is not running, or device is not
+mounted) the ``scan`` command is able to introspect the device to capture
+required data. Just like :ref:`ceph-volume-simple-scan-directory`, it would
+still require a few files present. This means that the device to be scanned
+**must be** the data partition of the OSD.
+
+As long as the data partition of the OSD is being passed in as an argument, the
+sub-command can scan its contents.
+
+In the case where the device is already mounted, the tool can detect this
+scenario and capture file contents from that directory.
+
+If the device is not mounted, a temporary directory will be created, and the
+device will be mounted temporarily just for scanning the contents. Once
+contents are scanned, the device will be unmounted.
+
+For a device like ``/dev/sda1`` which **must** be a data partition, the command
+could look like::
+
+    ceph-volume simple scan /dev/sda1
+
+
+.. _ceph-volume-simple-scan-json:
+
+``JSON`` contents
+-----------------
+The contents of the JSON object is very simple. The scan not only will persist
+information from the special OSD files and their contents, but will also
+validate paths and device UUIDs. Unlike what ``ceph-disk`` would do, by storing
+them in ``{device type}_uuid`` files, the tool will persist them as part of the
+device type key.
+
+For example, a ``block.db`` device would look something like::
+
+    "block.db": {
+        "path": "/dev/disk/by-partuuid/6cc43680-4f6e-4feb-92ff-9c7ba204120e",
+        "uuid": "6cc43680-4f6e-4feb-92ff-9c7ba204120e"
+    },
+
+But it will also persist the ``ceph-disk`` special file generated, like so::
+
+    "block.db_uuid": "6cc43680-4f6e-4feb-92ff-9c7ba204120e",
+
+This duplication is in place because the tool is trying to ensure the
+following:
+
+# Support OSDs that may not have ceph-disk special files
+# Check the most up-to-date information on the device, by querying against LVM
+and ``blkid``
+# Support both logical volumes and GPT devices
+
+This is a sample ``JSON`` metadata, from an OSD that is using ``bluestore``::
+
+    {
+        "active": "ok",
+        "block": {
+            "path": "/dev/disk/by-partuuid/40fd0a64-caa5-43a3-9717-1836ac661a12",
+            "uuid": "40fd0a64-caa5-43a3-9717-1836ac661a12"
+        },
+        "block.db": {
+            "path": "/dev/disk/by-partuuid/6cc43680-4f6e-4feb-92ff-9c7ba204120e",
+            "uuid": "6cc43680-4f6e-4feb-92ff-9c7ba204120e"
+        },
+        "block.db_uuid": "6cc43680-4f6e-4feb-92ff-9c7ba204120e",
+        "block_uuid": "40fd0a64-caa5-43a3-9717-1836ac661a12",
+        "bluefs": "1",
+        "ceph_fsid": "c92fc9eb-0610-4363-aafc-81ddf70aaf1b",
+        "cluster_name": "ceph",
+        "data": {
+            "path": "/dev/sdr1",
+            "uuid": "86ebd829-1405-43d3-8fd6-4cbc9b6ecf96"
+        },
+        "fsid": "86ebd829-1405-43d3-8fd6-4cbc9b6ecf96",
+        "keyring": "AQBBJ/dZp57NIBAAtnuQS9WOS0hnLVe0rZnE6Q==",
+        "kv_backend": "rocksdb",
+        "magic": "ceph osd volume v026",
+        "mkfs_done": "yes",
+        "ready": "ready",
+        "systemd": "",
+        "type": "bluestore",
+        "whoami": "3"
+    }