CDR File Directories

In its simplest form, the CDR scripts copy files from a directory on the DAQ system into a directory in CASTOR. Files for transfer are identified by a "tag" value which is specified in the CDR service request. CDR is controlled by a configuration file and this allows for some customisation for different experiments. For example, files in different directories on the DAQ can be transferred to different directories in CASTOR.

CDR writes log files of all transfers and files on the DAQ can be detected according to high and low watermarks specified in the configuration. Files are only deleted once they are physically written to permanent storage, or in other words, to a tape device. 

CDR Account

The CDR software is installed and runs under a unique account which will own the files subsequently transferred to CASTOR. The account must exist both on the data acquisition machine and be known in the central CERN account database. Both account must have the same Unix uid/gid combination for coherent ownership of files.  It is highly recommended that a local password file entry be used on the DAQ system so that CDR data recording independent of the AFS service. The CDR account name should not be used by other group members for interactive work.

DAQ configuration for CDR

All CDR data is written to CASTOR and there are requirements common to all DAQ systems:

• The CDR software is controlled by a crontab (or acrontab for AFS). Cron/acron must be running on the DAQ machine and the CDR account must have permission to execute cron jobs. The mechanisms for cron access or denial may not be the same for all UNIX variants.
  

• AFS is not required on data acquisition machines. All CDR scripts and executables are local and independent of the AFS file tree.
  

DAQ Storage Requirements

The data directory(s) on the data acquisition system are specified in the CDR configuration and are managed by the CDR scripts. They should be used exclusively for CDR activity with a size large enough to handle several days of data taking.

Ideally, the directory should be a mounted Unix file system . By using a reasonable disk data buffer, the CDR recording can be more resilient to network or CASTOR problems. It also means that data taking can continue over a weekend when CDR support may be at minimal level. Disks of 120GB are now commonplace and this kind of capacity is fine for most testbeam applications.

Operating Systems

CDR uses the rfcp file copy program to transfer data to CASTOR and therefore only runs on systems where rfio is supported. Supported OS platforms are AIX 4.3, Solaris 8, 9 and Linux SLC3 and other Linux versions.

Storage Costs

CDR data are written to STK9940B cartridges with 200GB capacity, 30MB/sec data transfer rate  and have a nominal cost of 120CHF.