OSD Service Specification¶
Service Specification 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
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
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
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.
[monitor.1]# ceph orch apply osd -i /path/to/osd_spec.yml --dry-run
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
You can also match by disk Size.
Size specification of format can be of form:
Includes disks of an exact size
Includes disks which size is within the range
Includes disks less than or equal to 10G in size
Includes disks equal to or greater than 40G in size
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
This operates on the ‘rotational’ attribute of the disk.
rotational: 0 | 1
1 to match all disks that are rotational
0 to match all disks that are non-rotational (SSD, NVME etc)
This will take all disks that are ‘available’
Note: This is exclusive for the data_devices section.
When you specified valid filters but want to limit the amount of matching disks you can use the ‘limit’ directive.
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.
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.
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.
service_type: osd service_id: example_osd_spec placement: host_pattern: '*' data_devices: all: true encrypted: true
See a full list in the DriveGroupSpecs
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:
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:
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:
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.
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.
20 HDDs Vendor: Intel Model: SSD-123-foo Size: 4TB 2 SSDs Vendor: VendorA Model: MC-55-44-ZX Size: 512GB
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.
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):
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.