Chapter 9. Management of MDS service using the Ceph Orchestrator

As a storage administrator, you can use Ceph Orchestrator with Cephadm in the backend to deploy the MDS service. By default, a Ceph File System (CephFS) uses only one active MDS daemon. However, systems with many clients benefit from multiple active MDS daemons.

This section covers the following administrative tasks:

Prerequisites

A running Red Hat Ceph Storage cluster.
Root-level access to all the nodes.
Hosts are added to the cluster.
All manager, monitor and OSD daemons are deployed.

9.1. Deploying the MDS service using the command line interface

Using the Ceph Orchestrator, you can deploy the Metadata Server (MDS) service using the placement specification in the command line interface. Ceph File System (CephFS) requires one or more MDS.

Note

Ensure you have at least two pools, one for Ceph file system (CephFS) data and one for CephFS metadata.

Prerequisites

A running Red Hat Ceph Storage cluster.
Hosts are added to the cluster.
All manager, monitor, and OSD daemons are deployed.

Procedure

Log into the Cephadm shell:
Example
```
[root@host01 ~]# cephadm shell
```
There are two ways of deploying MDS daemons using placement specification:

Method 1

Use ceph fs volume to create the MDS daemons. This creates the CephFS volume and pools associated with the CephFS, and also starts the MDS service on the hosts.
Syntax
```
ceph fs volume create FILESYSTEM_NAME --placement="NUMBER_OF_DAEMONS HOST_NAME_1 HOST_NAME_2 HOST_NAME_3"
```
Note
By default, replicated pools are created for this command.
Example
```
[ceph: root@host01 /]# ceph fs volume create test --placement="2 host01 host02"
```

Method 2

Create the pools, CephFS, and then deploy MDS service using placement specification:
1. Create the pools for CephFS:
  Syntax
```
ceph osd pool create DATA_POOL [PG_NUM]
ceph osd pool create METADATA_POOL [PG_NUM]
```
  Example
```
[ceph: root@host01 /]# ceph osd pool create cephfs_data 64
[ceph: root@host01 /]# ceph osd pool create cephfs_metadata 64
```
  Typically, the metadata pool can start with a conservative number of Placement Groups (PGs) as it generally has far fewer objects than the data pool. It is possible to increase the number of PGs if needed. The pool sizes range from 64 PGs to 512 PGs. Size the data pool is proportional to the number and sizes of files you expect in the file system.
  Important
  For the metadata pool, consider to use:
  A higher replication level because any data loss to this pool can make the whole file system inaccessible.
  Storage with lower latency such as Solid-State Drive (SSD) disks because this directly affects the observed latency of file system operations on clients.
2. Create the file system for the data pools and metadata pools:
  Syntax
```
ceph fs new FILESYSTEM_NAME METADATA_POOL DATA_POOL
```
  Example
```
[ceph: root@host01 /]# ceph fs new test cephfs_metadata cephfs_data
```
3. Deploy MDS service using the ceph orch apply command:
  Syntax
```
ceph orch apply mds FILESYSTEM_NAME --placement="NUMBER_OF_DAEMONS HOST_NAME_1 HOST_NAME_2 HOST_NAME_3"
```
  Example
```
[ceph: root@host01 /]# ceph orch apply mds test --placement="2 host01 host02"
```

Verification

List the service:
Example
```
[ceph: root@host01 /]# ceph orch ls
```

Check the CephFS status:

Example

[ceph: root@host01 /]# ceph fs ls
[ceph: root@host01 /]# ceph fs status

List the hosts, daemons, and processes:

Syntax

ceph orch ps --daemon_type=DAEMON_NAME

Example

[ceph: root@host01 /]# ceph orch ps --daemon_type=mds

Additional Resources

See the Red Hat Ceph Storage File System Guide for more information about creating the Ceph File System (CephFS).
For information on setting the pool values, see Setting number of placement groups in a pool.

9.2. Deploying the MDS service using the service specification

Using the Ceph Orchestrator, you can deploy the MDS service using the service specification.

Note

Ensure you have at least two pools, one for the Ceph File System (CephFS) data and one for the CephFS metadata.

Prerequisites

A running Red Hat Ceph Storage cluster.
Hosts are added to the cluster.
All manager, monitor, and OSD daemons are deployed.

Procedure

Create the mds.yaml file:
Example
```
[root@host01 ~]# touch mds.yaml
```

Edit the mds.yaml file to include the following details:

Syntax

service_type: mds
service_id: FILESYSTEM_NAME
placement:
  hosts:
  - HOST_NAME_1
  - HOST_NAME_2
  - HOST_NAME_3

Example

service_type: mds
service_id: fs_name
placement:
  hosts:
  - host01
  - host02

Mount the YAML file under a directory in the container:

Example

[root@host01 ~]# cephadm shell --mount mds.yaml:/var/lib/ceph/mds/mds.yaml

Navigate to the directory:

Example

[ceph: root@host01 /]# cd /var/lib/ceph/mds/

Log into the Cephadm shell:
Example
```
[root@host01 ~]# cephadm shell
```

Navigate to the following directory:

Example

[ceph: root@host01 /]# cd /var/lib/ceph/mds/

Deploy MDS service using service specification:

Syntax

ceph orch apply -i FILE_NAME.yaml

Example

[ceph: root@host01 mds]# ceph orch apply -i mds.yaml

Once the MDS services is deployed and functional, create the CephFS:

Syntax

ceph fs new CEPHFS_NAME METADATA_POOL DATA_POOL

Example

[ceph: root@host01 /]# ceph fs new test metadata_pool data_pool

Verification

List the service:
Example
```
[ceph: root@host01 /]# ceph orch ls
```

List the hosts, daemons, and processes:

Syntax

ceph orch ps --daemon_type=DAEMON_NAME

Example

[ceph: root@host01 /]# ceph orch ps --daemon_type=mds

Additional Resources

See the Red Hat Ceph Storage File System Guide for more information about creating the Ceph File System (CephFS).

9.3. Removing the MDS service using the Ceph Orchestrator

You can remove the service using the ceph orch rm command. Alternatively, you can remove the file system and the associated pools.

Prerequisites

A running Red Hat Ceph Storage cluster.
Root-level access to all the nodes.
Hosts are added to the cluster.
At least one MDS daemon deployed on the hosts.

Procedure

There are two ways of removing MDS daemons from the cluster:

Method 1

Remove the CephFS volume, associated pools, and the services:
1. Log into the Cephadm shell:
  Example
```
[root@host01 ~]# cephadm shell
```
2. Set the configuration parameter mon_allow_pool_delete to true:
  Example
```
[ceph: root@host01 /]# ceph config set mon mon_allow_pool_delete true
```
3. Remove the file system:
  Syntax
```
ceph fs volume rm FILESYSTEM_NAME --yes-i-really-mean-it
```
  Example
```
[ceph: root@host01 /]# ceph fs volume rm cephfs-new --yes-i-really-mean-it
```
  This command will remove the file system, its data, and metadata pools. It also tries to remove the MDS using the enabled ceph-mgr Orchestrator module.

Method 2

Use the ceph orch rm command to remove the MDS service from the entire cluster:
1. List the service:
  Example
```
[ceph: root@host01 /]# ceph orch ls
```
2. Remove the service
  Syntax
```
ceph orch rm SERVICE_NAME
```
  Example
```
[ceph: root@host01 /]# ceph orch rm mds.test
```

Verification

List the hosts, daemons, and processes:
Syntax
```
ceph orch ps
```
Example
```
[ceph: root@host01 /]# ceph orch ps
```

Additional Resources

See Deploying the MDS service using the command line interface section in the Red Hat Ceph Storage Operations Guide for more information.
See Deploying the MDS service using the service specification section in the Red Hat Ceph Storage Operations Guide for more information.

Chapter 9. Management of MDS service using the Ceph Orchestrator

9.1. Deploying the MDS service using the command line interface

9.2. Deploying the MDS service using the service specification

9.3. Removing the MDS service using the Ceph Orchestrator

Learn

Try, buy, & sell

Communities

About Red Hat Documentation

Making open source more inclusive

About Red Hat

Red Hat legal and privacy links

Red Hat legal and privacy links