Terminology¶

An overview of terms used in the context of EESSI, in alphabetical order.

CernVM-FS¶

Client¶

A client in the context of CernVM-FS is a computer system on which a CernVM-FS repository is being accessed, on which it will be presented as a POSIX read-only file system in a subdirectory of /cvmfs.

Proxy¶

A proxy, also referred to as squid proxy, is a forward caching proxy server which acts as an intermediary between a CernVM-FS client and the Stratum-1 replica servers.

It is used to improve the latency observed when accessing the contents of a repository, and to reduce the load on the Stratum-1 replica servers.

A commonly used proxy is Squid.

For more information on proxies, see the CernVM-FS documentation.

Repository¶

A CernVM-FS repository is where the files and directories that you want to distribute via CernVM-FS are stored, which usually correspond to a collection of software installations.

It is a form of content-addressable storage (CAS), and is the single source of (new) data for the file system being presented as a subdirectory of /cvmfs on client systems that mount the repository.

Note

A CernVM-FS repository includes software installations, not software packages like RPMs.

Software installations¶

An important distinction for a CernVM-FS repository compared to the more traditional notion of a software repository is that a CernVM-FS repository provides access to the individual files that collectively form a particular software installation, as opposed to housing a set of software packages like RPMs, each of which being a collection of files for a particular software installation that are packed together in a single package to distribute as a whole.

Note

This is an important distinction, since CernVM-FS enables only downloading the specific files that are required to perform a particular task with a software installation, which often is a small subset of all files that are part of that software installation.

Stratum 1 replica server¶

A Stratum 1 replica server, often simply referred to a Stratum 1 (Stratum One), is a standard web server that acts as a mirror server for one or more CernVM-FS repositories.

It holds a complete copy of the data for each CernVM-FS repository it serves, and automatically synchronises with the main Stratum 0.

There is typically a network of several Stratum 1 servers for a CernVM-FS repository, which are geographically distributed.

Clients can be configured to automatically connect to the closest Stratum 1 server by using the CernVM-FS GeoAPI.

For more information, see the CernVM-FS documentation.