File system components
The Ceph File System is comprised of clients and Metadata Servers (MDS). Understand the component layers of the Ceph File system and the underlying core storage cluster components.
The Ceph File System has two primary components:
- Clients
- The CephFS clients perform I/O operations on behalf of applications using CephFS, such as
ceph-fusefor FUSE clients andkcephfsfor kernel clients. CephFS clients send metadata requests to an active Metadata Server. In return, the CephFS client learns of the file metadata, and can begin safely caching both metadata and file data. - Metadata Servers (MDS)
- The MDS does the following:
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Provides metadata to CephFS clients.
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Manages metadata related to files stored on the Ceph File System.
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Coordinates access to the shared IBM Storage Ceph cluster.
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Caches hot metadata to reduce requests to the backing metadata pool store.
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Manages the CephFS clients' caches to maintain cache coherence.
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Replicates hot metadata between active MDS.
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Coalesces metadata mutations to a compact journal with regular flushes to the backing metadata pool.
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CephFS requires at least one Metadata Server daemon (
ceph-mds) to run.
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Ceph File System components can be divided into four layers, as illustrated in Figure 1.
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Ceph OSDs (
ceph-osd) where the Ceph File System data and metadata are stored. -
Ceph Metadata Servers (
ceph-mds) that manages Ceph File System metadata. -
Ceph Monitors (
ceph-mon) that manages the master copy of the cluster map.
Next is the Ceph Storage protocol layer. This represents the Ceph native
librados library for interacting with the core storage cluster.
The CephFS library layer includes the CephFS libcephfs library that works on top
of librados and represents the Ceph File System.
The top layer represents the two types of Ceph clients that can access the Ceph File Systems: CephFS kernel object and CephFS FUSE.
