ceph/doc/cephadm/drivegroups.rst
Joshua Schmid a8e21a114b doc: add notes about --dry-run
Signed-off-by: Joshua Schmid <jschmid@suse.de>
2020-07-22 16:01:56 +02:00

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.. _drivegroups:
=========================
OSD Service Specification
=========================
:ref:`orchestrator-cli-service-spec` of type ``osd`` are a way to describe a cluster layout using the properties of disks.
It gives the user an abstract way tell ceph which disks should turn into an OSD
with which configuration without knowing the specifics of device names and paths.
Instead of doing this::
[monitor 1] # ceph orch daemon add osd *<host>*:*<path-to-device>*
for each device and each host, we can define a yaml|json file that allows us to describe
the layout. Here's the most basic example.
Create a file called i.e. osd_spec.yml
.. code-block:: yaml
service_type: osd
service_id: default_drive_group <- name of the drive_group (name can be custom)
placement:
host_pattern: '*' <- which hosts to target, currently only supports globs
data_devices: <- the type of devices you are applying specs to
all: true <- a filter, check below for a full list
This would translate to:
Turn any available(ceph-volume decides what 'available' is) into an OSD on all hosts that match
the glob pattern '*'. (The glob pattern matches against the registered hosts from `host ls`)
There will be a more detailed section on host_pattern down below.
and pass it to `osd create` like so::
[monitor 1] # ceph orch apply osd -i /path/to/osd_spec.yml
This will go out on all the matching hosts and deploy these OSDs.
Since we want to have more complex setups, there are more filters than just the 'all' filter.
Also, there is a `--dry-run` flag that can be passed to the `apply osd` command, which gives you a synopsis
of the proposed layout.
Example::
[monitor 1] # ceph orch apply osd -i /path/to/osd_spec.yml --dry-run
Filters
=======
.. note::
Filters are applied using a `AND` gate by default. This essentially means that a drive needs to fulfill all filter
criteria in order to get selected.
If you wish to change this behavior you can adjust this behavior by setting
`filter_logic: OR` # valid arguments are `AND`, `OR`
in the OSD Specification.
You can assign disks to certain groups by their attributes using filters.
The attributes are based off of ceph-volume's disk query. You can retrieve the information
with::
ceph-volume inventory </path/to/disk>
Vendor or Model:
-------------------
You can target specific disks by their Vendor or by their Model
.. code-block:: yaml
model: disk_model_name
or
.. code-block:: yaml
vendor: disk_vendor_name
Size:
--------------
You can also match by disk `Size`.
.. code-block:: yaml
size: size_spec
Size specs:
___________
Size specification of format can be of form:
* LOW:HIGH
* :HIGH
* LOW:
* EXACT
Concrete examples:
Includes disks of an exact size::
size: '10G'
Includes disks which size is within the range::
size: '10G:40G'
Includes disks less than or equal to 10G in size::
size: ':10G'
Includes disks equal to or greater than 40G in size::
size: '40G:'
Sizes don't have to be exclusively in Gigabyte(G).
Supported units are Megabyte(M), Gigabyte(G) and Terrabyte(T). Also appending the (B) for byte is supported. MB, GB, TB
Rotational:
-----------
This operates on the 'rotational' attribute of the disk.
.. code-block:: yaml
rotational: 0 | 1
`1` to match all disks that are rotational
`0` to match all disks that are non-rotational (SSD, NVME etc)
All:
------------
This will take all disks that are 'available'
Note: This is exclusive for the data_devices section.
.. code-block:: yaml
all: true
Limiter:
--------
When you specified valid filters but want to limit the amount of matching disks you can use the 'limit' directive.
.. code-block:: yaml
limit: 2
For example, if you used `vendor` to match all disks that are from `VendorA` but only want to use the first two
you could use `limit`.
.. code-block:: yaml
data_devices:
vendor: VendorA
limit: 2
Note: Be aware that `limit` is really just a last resort and shouldn't be used if it can be avoided.
Additional Options
===================
There are multiple optional settings you can use to change the way OSDs are deployed.
You can add these options to the base level of a DriveGroup for it to take effect.
This example would deploy all OSDs with encryption enabled.
.. code-block:: yaml
service_type: osd
service_id: example_osd_spec
placement:
host_pattern: '*'
data_devices:
all: true
encrypted: true
See a full list in the DriveGroupSpecs
.. py:currentmodule:: ceph.deployment.drive_group
.. autoclass:: DriveGroupSpec
:members:
:exclude-members: from_json
Examples
========
The simple case
---------------
All nodes with the same setup::
20 HDDs
Vendor: VendorA
Model: HDD-123-foo
Size: 4TB
2 SSDs
Vendor: VendorB
Model: MC-55-44-ZX
Size: 512GB
This is a common setup and can be described quite easily:
.. code-block:: yaml
service_type: osd
service_id: osd_spec_default
placement:
host_pattern: '*'
data_devices:
model: HDD-123-foo <- note that HDD-123 would also be valid
db_devices:
model: MC-55-44-XZ <- same here, MC-55-44 is valid
However, we can improve it by reducing the filters on core properties of the drives:
.. code-block:: yaml
service_type: osd
service_id: osd_spec_default
placement:
host_pattern: '*'
data_devices:
rotational: 1
db_devices:
rotational: 0
Now, we enforce all rotating devices to be declared as 'data devices' and all non-rotating devices will be used as shared_devices (wal, db)
If you know that drives with more than 2TB will always be the slower data devices, you can also filter by size:
.. code-block:: yaml
service_type: osd
service_id: osd_spec_default
placement:
host_pattern: '*'
data_devices:
size: '2TB:'
db_devices:
size: ':2TB'
Note: All of the above DriveGroups are equally valid. Which of those you want to use depends on taste and on how much you expect your node layout to change.
The advanced case
-----------------
Here we have two distinct setups::
20 HDDs
Vendor: VendorA
Model: HDD-123-foo
Size: 4TB
12 SSDs
Vendor: VendorB
Model: MC-55-44-ZX
Size: 512GB
2 NVMEs
Vendor: VendorC
Model: NVME-QQQQ-987
Size: 256GB
* 20 HDDs should share 2 SSDs
* 10 SSDs should share 2 NVMes
This can be described with two layouts.
.. code-block:: yaml
service_type: osd
service_id: osd_spec_hdd
placement:
host_pattern: '*'
data_devices:
rotational: 0
db_devices:
model: MC-55-44-XZ
limit: 2 (db_slots is actually to be favoured here, but it's not implemented yet)
service_type: osd
service_id: osd_spec_ssd
placement:
host_pattern: '*'
data_devices:
model: MC-55-44-XZ
db_devices:
vendor: VendorC
This would create the desired layout by using all HDDs as data_devices with two SSD assigned as dedicated db/wal devices.
The remaining SSDs(8) will be data_devices that have the 'VendorC' NVMEs assigned as dedicated db/wal devices.
The advanced case (with non-uniform nodes)
------------------------------------------
The examples above assumed that all nodes have the same drives. That's however not always the case.
Node1-5::
20 HDDs
Vendor: Intel
Model: SSD-123-foo
Size: 4TB
2 SSDs
Vendor: VendorA
Model: MC-55-44-ZX
Size: 512GB
Node6-10::
5 NVMEs
Vendor: Intel
Model: SSD-123-foo
Size: 4TB
20 SSDs
Vendor: VendorA
Model: MC-55-44-ZX
Size: 512GB
You can use the 'host_pattern' key in the layout to target certain nodes. Salt target notation helps to keep things easy.
.. code-block:: yaml
service_type: osd
service_id: osd_spec_node_one_to_five
placement:
host_pattern: 'node[1-5]'
data_devices:
rotational: 1
db_devices:
rotational: 0
service_type: osd
service_id: osd_spec_six_to_ten
placement:
host_pattern: 'node[6-10]'
data_devices:
model: MC-55-44-XZ
db_devices:
model: SSD-123-foo
This applies different OSD specs to different hosts depending on the `host_pattern` key.
Dedicated wal + db
------------------
All previous cases co-located the WALs with the DBs.
It's however possible to deploy the WAL on a dedicated device as well, if it makes sense.
::
20 HDDs
Vendor: VendorA
Model: SSD-123-foo
Size: 4TB
2 SSDs
Vendor: VendorB
Model: MC-55-44-ZX
Size: 512GB
2 NVMEs
Vendor: VendorC
Model: NVME-QQQQ-987
Size: 256GB
The OSD spec for this case would look like the following (using the `model` filter):
.. code-block:: yaml
service_type: osd
service_id: osd_spec_default
placement:
host_pattern: '*'
data_devices:
model: MC-55-44-XZ
db_devices:
model: SSD-123-foo
wal_devices:
model: NVME-QQQQ-987
This can easily be done with other filters, like `size` or `vendor` as well.