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Comment: clarify some points in the document

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A Client in the Lustre filesystem is a machine that requires data. This could be a computation, visualisationvisualization, or desktop node. Once mounted, a Client experiences the Lustre filesystem as if the filesystem were a local or NFS mount.

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In the Lustre filesystem metadata requests are serviced by two components: the Metadata Server (MDS, a server node) an Metadata Target (MDT, the HDD/SSD that stores the metadata). Together, the MDS and MDT service requests like: Where is the data for file XYZ located? Do I 'm going have permission to write to file ABC so prohibit anyone else from using it.?

All a Client needs to mount a Lustre filesystem is the location of the MDS. Currently, each Lustre filesystem has only one active MDS. The MDS persists the filesystem metadata in the MDT.

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Data in the Lustre filesystem is stored and retrieved by two components: the Object Storage Server (OSS, a server node) and the Object Storage Target (OST, the HDD/SSD that stores the data). Together, the OSS and OST provide the data to the Client.

A Lustre filesystem can have one or more OSS nodes. An OSS typically has between two and eight OSTs attached. To increase the storage capacity of the Lustre filesystem, additional OSTs can be attached. To increase the bandwidth of the Lustre filesystem, additional OSS can be attached – provided the connection to the Client is not saturated.

Further reading:

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Networking

Lustre includes additional services including LNETuses LNET to configure and communicate over the network between clients and servers. LNET is designed to simplify configuration of a Lustre filesystem over complex network topologiesprovide maximum performance over a variety of different network types, including InfiniBand, Ethernet, and networks inside HPC clusters such as Cray XP/XE systems.

Further reading:

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Lustre currently has two actively developed and maintained branches. These the are 1.8.x and 2.1 releases. Lustre 1.8.x is used in production environments around the world. It is mature and stable. Lustre 2.1 introduces SMP scaling enhancements to exploit machines with large numbers of sockets, cores and threads. The Lustre 2.1 release is scheduled at the end of Q2, 2011  There are also feature releases of Lustre that are available to try out new features of Lustre, but will not have long term maintenance releases.

The Metadata Server (MDS) is crucial to overall performance of the Lustre filesystem. Increasing memory on the MDS will increase the cache available and increase performance for filesystems with many files. It is common to see production MDS machines boast 24GB or 48GB per core.

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