ceph/doc/ceph-volume/lvm/batch.rst

.. _ceph-volume-lvm-batch:

``batch``
===========
The subcommand allows to create multiple OSDs at the same time given
an input of devices. The ``batch`` subcommand is closely related to
drive-groups. One individual drive group specification translates to a single
``batch`` invocation.

The subcommand is based to :ref:`ceph-volume-lvm-create`, and will use the very
same code path. All ``batch`` does is to calculate the appropriate sizes of all
volumes and skip over already created volumes.

All the features that ``ceph-volume lvm create`` supports, like ``dmcrypt``,
avoiding ``systemd`` units from starting, defining bluestore,
is supported.


.. _ceph-volume-lvm-batch_auto:

Automatic sorting of disks
--------------------------
If ``batch`` receives only a single list of data devices and other options are
passed , ``ceph-volume`` will auto-sort disks by its rotational
property and use non-rotating disks for ``block.db`` or ``journal`` depending
on the objectstore used. If all devices are to be used for standalone OSDs,
no matter if rotating or solid state, pass ``--no-auto``.
For example assuming :term:`bluestore` is used and ``--no-auto`` is not passed,
the deprecated behavior would deploy the following, depending on the devices
passed:

#. Devices are all spinning HDDs: 1 OSD is created per device
#. Devices are all SSDs: 2 OSDs are created per device
#. Devices are a mix of HDDs and SSDs: data is placed on the spinning device,
   the ``block.db`` is created on the SSD, as large as possible.

.. note:: Although operations in ``ceph-volume lvm create`` allow usage of
          ``block.wal`` it isn't supported with the ``auto`` behavior.

This default auto-sorting behavior is now DEPRECATED and will be changed in future releases.
Instead devices are not automatically sorted unless the ``--auto`` option is passed

It is recommended to make use of the explicit device lists for ``block.db``,
   ``block.wal`` and ``journal``.

.. _ceph-volume-lvm-batch_bluestore:

Reporting
=========
By default ``batch`` will print a report of the computed OSD layout and ask the
user to confirm. This can be overridden by passing ``--yes``.

If one wants to try out several invocations with being asked to deploy
``--report`` can be passed. ``ceph-volume`` will exit after printing the report.

Consider the following invocation::

    $ ceph-volume lvm batch --report /dev/sdb /dev/sdc /dev/sdd --db-devices /dev/nvme0n1

This will deploy three OSDs with external ``db`` and ``wal`` volumes on
an NVME device.

Pretty reporting
----------------

The ``pretty`` report format (the default) would
look like this::

    $ ceph-volume lvm batch --report /dev/sdb /dev/sdc /dev/sdd --db-devices /dev/nvme0n1
    --> passed data devices: 3 physical, 0 LVM
    --> relative data size: 1.0
    --> passed block_db devices: 1 physical, 0 LVM

    Total OSDs: 3

      Type            Path                                                    LV Size         % of device
    ----------------------------------------------------------------------------------------------------
      data            /dev/sdb                                              300.00 GB         100.00%
      block_db        /dev/nvme0n1                                           66.67 GB         33.33%
    ----------------------------------------------------------------------------------------------------
      data            /dev/sdc                                              300.00 GB         100.00%
      block_db        /dev/nvme0n1                                           66.67 GB         33.33%
    ----------------------------------------------------------------------------------------------------
      data            /dev/sdd                                              300.00 GB         100.00%
      block_db        /dev/nvme0n1                                           66.67 GB         33.33%


JSON reporting
--------------

Reporting can produce a structured output with ``--format json`` or
``--format json-pretty``::

    $ ceph-volume lvm batch --report --format json-pretty /dev/sdb /dev/sdc /dev/sdd --db-devices /dev/nvme0n1
    --> passed data devices: 3 physical, 0 LVM
    --> relative data size: 1.0
    --> passed block_db devices: 1 physical, 0 LVM
    [
        {
            "block_db": "/dev/nvme0n1",
            "block_db_size": "66.67 GB",
            "data": "/dev/sdb",
            "data_size": "300.00 GB",
            "encryption": "None"
        },
        {
            "block_db": "/dev/nvme0n1",
            "block_db_size": "66.67 GB",
            "data": "/dev/sdc",
            "data_size": "300.00 GB",
            "encryption": "None"
        },
        {
            "block_db": "/dev/nvme0n1",
            "block_db_size": "66.67 GB",
            "data": "/dev/sdd",
            "data_size": "300.00 GB",
            "encryption": "None"
        }
    ]

Sizing
======
When no sizing arguments are passed, `ceph-volume` will derive the sizing from
the passed device lists (or the sorted lists when using the automatic sorting).
`ceph-volume batch` will attempt to fully utilize a device's available capacity.
Relying on automatic sizing is recommended.

If one requires a different sizing policy for wal, db or journal devices,
`ceph-volume` offers implicit and explicit sizing rules.

Implicit sizing
---------------
Scenarios in which either devices are under-committed or not all data devices are
currently ready for use (due to a broken disk for example), one can still rely
on `ceph-volume` automatic sizing.
Users can provide hints to `ceph-volume` as to how many data devices should have
their external volumes on a set of fast devices. These options are:

* ``--block-db-slots``
* ``--block-wal-slots``
* ``--journal-slots``

For example, consider an OSD host that is supposed to contain 5 data devices and
one device for wal/db volumes. However, one data device is currently broken and
is being replaced. Instead of calculating the explicit sizes for the wal/db
volume, one can simply call::

    $ ceph-volume lvm batch --report /dev/sdb /dev/sdc /dev/sdd /dev/sde --db-devices /dev/nvme0n1 --block-db-slots 5

Explicit sizing
---------------
It is also possible to provide explicit sizes to `ceph-volume` via the arguments

* ``--block-db-size``
* ``--block-wal-size``
* ``--journal-size``

`ceph-volume` will try to satisfy the requested sizes given the passed disks. If
this is not possible, no OSDs will be deployed.


Idempotency and disk replacements
=================================
`ceph-volume lvm batch` intends to be idempotent, i.e. calling the same command
repeatedly must result in the same outcome. For example calling::

    $ ceph-volume lvm batch --report /dev/sdb /dev/sdc /dev/sdd --db-devices /dev/nvme0n1

will result in three deployed OSDs (if all disks were available). Calling this
command again, you will still end up with three OSDs and ceph-volume will exit
with return code 0.

Suppose /dev/sdc goes bad and needs to be replaced. After destroying the OSD and
replacing the hardware, you can again call the same command and `ceph-volume`
will detect that only two out of the three wanted OSDs are setup and re-create
the missing OSD.

This idempotency notion is tightly coupled to and extensively used by :ref:`drivegroups`.