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Chapter 4. Chimera

dCache is a distributed storage system, nevertheless it provides a single-rooted file system view. While dCache supports multiple namespace providers, Chimera is the recommended provider and is used by default.

The inner dCache components talk to the namespace via a module called PnfsManager, which in turn communicates with the Chimera database using a thin Java layer, which in turn communicates directly with the Chimera database. Chimera allows direct access to the namespace by providing an NFSv3 and NFSv4.1 server. Clients can NFS-mount the namespace locally. This offers the opportunity to use OS-level tools like ls, mkdir, mv for Chimera. Direct I/O-operations like cp and cat are possible with the NFSv4.1 door.

The properties of Chimera are defined in /usr/share/dcache/defaults/chimera.properties. For customisation the files /etc/dcache/layouts/mylayout.conf or /etc/dcache/dcache.conf should be modified (see the section called “Defining domains and services”).

Example:

This example shows an extract of the /etc/dcache/layouts/mylayout.conf file in order to run dCache with NFSv3.

[namespaceDomain]
[namespaceDomain/pnfsmanager]
[namespaceDomain/nfs]
nfs.version=3

Example:

If you want to run the NFSv4.1 server you need to add the corresponding nfs service to a domain in the /etc/dcache/layouts/mylayout.conf file and start this domain.

[namespaceDomain]
[namespaceDomain/pnfsmanager]
[namespaceDomain/nfs]
nfs.version = 4.1

If you wish dCache to access your Chimera with a PostgreSQL user other than chimera then you must specify the username and password in /etc/dcache/dcache.conf.

chimera.db.user=myuser
chimera.db.password=secret

Important

Do not update configuration values in /usr/share/dcache/defaults/chimera.properties, since changes to this file will be overwritten by updates.