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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.