Client features

At times you might want to set Ceph File System (CephFS) features that clients must support to enable them to use Ceph File Systems. Clients without these features might disrupt other CephFS clients, or behave in unexpected ways. Also, you might want to require new features to prevent older, and possibly buggy clients from connecting to a Ceph File System.

Important: CephFS clients missing newly added features are evicted automatically. You can list all the CephFS features by using the fs features ls command. You can add or remove requirements by using the fs required_client_features command.

Use the following syntax:

fs required_client_features FILE_SYSTEM_NAME add FEATURE_NAME
fs required_client_features FILE_SYSTEM_NAME rm FEATURE_NAME

Table 1. Client features
Client feature	Description
`reply_encoding`	The Ceph Metadata Server (MDS) encodes reply requests in extensible format, if the client supports this feature.
`reclaim_client`	The Ceph MDS allows a new client to reclaim another, perhaps a dead, client’s state. This feature is used by NFS service.
`lazy_caps_wanted`	When a stale client resumes, the Ceph MDS only needs to re-issue the capabilities that are explicitly wanted, if the client supports this feature.
`multi_reconnect`	After a Ceph MDS failover event, the client sends a reconnect message to the MDS to reestablish cache states. A client can split large reconnect messages into multiple messages.
`deleg_ino`	A Ceph MDS delegates inode numbers to a client, if the client supports this feature. Delegating inode numbers is a prerequisite for a client to do async file creation.
`metric_collect`	CephFS clients can send performance metrics to a Ceph MDS.
`alternate_name`	CephFS clients can set and understand alternative names for directory entries. This feature allows for encrypted file names.