Lustre組件

Lustre Components

An installation of the Lustre software includes a management server (MGS) and one or more Lustre file systems interconnected with Lustre networking (LNet).
A basic configuration of Lustre file system components is shown in “Lustre file system components in a basic cluster”.

Lustre file system components in a basic cluster

Management Server (MGS)

The MGS stores configuration information for all the Lustre file systems in a cluster and provides this information to other Lustre components. Each Lustre target contacts the MGS to provide information, and Lustre clients contact the MGS to retrieve information.
It is preferable that the MGS have its own storage space so that it can be managed independently. However, the MGS can be co-located and share storage space with an MDS as shown in Figure 1.1, “Lustre file system components in a basic cluster”.

Lustre File System Components

Each Lustre file system consists of the following components:

• Metadata Servers (MDS)
  The MDS makes metadata stored in one or more MDTs available to Lustre clients. Each MDS manages the names and directories in the Lustre file system(s) and provides network request handling for one or more local MDTs.

• Metadata Targets (MDT)
  Each filesystem has at least one MDT. The MDT stores metadata (such as filenames, directories, permissions and file layout) on storage attached to an MDS. Each file system has one MDT. An MDT on a shared storage target can be available to multiple MDSs, although only one can access it at a time. If an active MDS fails, a standby MDS can serve the MDT and make it available to clients. This is referred to as MDS failover.
  Multiple MDTs are supported in the Distributed Namespace Environment (DNE). In addition to the primary MDT that holds the filesystem root, it is possible to add additional MDS nodes, each with their own MDTs, to hold sub-directory trees of the filesystem.

• Object Storage Servers (OSS): The OSS provides file I/O service and network request handling for one or more local OSTs. Typically, an OSS serves between two and eight OSTs, up to 16 TiB each. A typical configuration is an MDT on a dedicated node, two or more OSTs on each OSS node, and a client on each of a large number of compute nodes.

• Object Storage Target (OST): User file data is stored in one or more objects, each object on a separate OST in a Lustre file system. The number of objects per file is configurable by the user and can be tuned to optimize performance for a given workload.

• Lustre clients: Lustre clients are computational, visualization or desktop nodes that are running Lustre client software, allowing them to mount the Lustre file system.

  The Lustre client software provides an interface between the Linux virtual file system and the Lustre servers. The client software includes a management client (MGC), a metadata client (MDC), and multiple object storage clients (OSCs), one corresponding to each OST in the file system.
  A logical object volume (LOV) aggregates the OSCs to provide transparent access across all the OSTs. Thus, a client with the Lustre file system mounted sees a single, coherent, synchronized namespace. Several clients can write to different parts of the same file simultaneously, while, at the same time, other clients can read from the file.
  A logical metadata volume (LMV) aggregates the MDCs to provide transparent access across all the MDTs in a similar manner as the LOV does for file access. This allows the client to see the directory tree on multiple MDTs as a single coherent namespace, and striped directories are merged on the clients to form a single visible directory to users and applications.

  Table 1.2, “ Storage and hardware requirements for Lustre file system components”provides the requirements for attached storage for each Lustre file system component and describes desirable characteristics of the hardware used.

  Storage and hardware requirements for Lustre file system components

  	Required attached storage	Desirable hardware characteristics
  MDSs	1-2% of file system capacity	Adequate CPU power, plenty of memory, fast disk storage.
  OSSs	1-128 TiB per OST, 1-8 OSTs per OSS	Good bus bandwidth. Recommended that storage be balanced evenly across OSSs and matched to network bandwidth.
  Clients	No local storage needed	Low latency, high bandwidth network

Lustre Networking (LNet)

Lustre Networking (LNet) is a custom networking API that provides the communication infrastructure that handles metadata and file I/O data for the Lustre file system servers and clients. For more information about LNet, see Chapter 2, Understanding Lustre Networking (LNet).

Lustre Cluster

At scale, a Lustre file system cluster can include hundreds of OSSs and thousands of clients (see Figure 1.2, “ Lustre cluster at scale”). More than one type of network can be used in a Lustre cluster. Shared storage between OSSs enables failover capability. For more details about OSS failover, see Chapter 3, Understanding Failover in a Lustre File System.

Lustre cluster at scale

Lustre client requesting file data