Configuring multiple active Metadata Server daemons

Configure multiple active Metadata Server (MDS) daemons to scale metadata performance for large systems.

Before you begin

Before you begin, make sure that you have the following prerequisites in place:

Ceph administration capabilities on the MDS node.
Root-level access to a Ceph Monitor node.

About this task

Important: Do not convert all standby MDS daemons to active ones. A Ceph File System (CephFS) requires at least one standby MDS daemon to remain highly available.

Procedure

Set the max_mds parameter to the desired number of active MDS daemons.
```
ceph fs set NAME max_mds NUMBER
```
For example, to increase the number of active MDS daemons to two in the CephFS called cephfs:
```
[root@mon ~]# ceph fs set cephfs max_mds 2
```
Note: Ceph only increases the actual number of ranks in the CephFS if a spare MDS daemon is available to take the new rank.

Verify the number of active MDS daemons.

ceph fs status NAME

For example:

[root@mon ~]# ceph fs status cephfs
cephfs - 0 clients
======
+------+--------+-------+---------------+-------+-------+--------+--------+
| RANK | STATE  |  MDS  |    ACTIVITY   |  DNS  |  INOS |  DIRS  |  CAPS  |
+------+--------+-------+---------------+-------+-------+--------+--------+
|  0   | active | node1 | Reqs:    0 /s |   10  |   12  |   12   |   0    |
|  1   | active | node2 | Reqs:    0 /s |   10  |   12  |   12   |   0    |
+------+--------+-------+---------------+-------+-------+--------+--------+
+-----------------+----------+-------+-------+
|       POOL      |   TYPE   |  USED | AVAIL |
+-----------------+----------+-------+-------+
| cephfs_metadata | metadata | 4638  | 26.7G |
|   cephfs_data   |   data   |    0  | 26.7G |
+-----------------+----------+-------+-------+

+-------------+
| STANDBY MDS |
+-------------+
|    node3    |
+-------------+