Access rights

All volumes (special case of AFS is described in separate article) are covered by standard set of unix permissions. Default set up of directories (including the home directory) and files is 755, ie. rwxr-xr-x. In case you want to change this behavior you can do it by invoking command

chmod 700 <directory>

To change the rights for your home directory and for computing/temporal directory (scratch) use

chmod 700 /home/$USER
chmod 700 $SCRATCHDIR

Changing the rights can be performed also from user scripts if you compute some sensitive data. On the other hand you can use current properties allowing read and execute to share your scripts in groups of users.

Backup policy of the /home volume

The /storage  volume is proof against an accidental failure of any of its hard drives. For long-term data protection or a protection of crucial data, please, store your data in the MetaCentrum's backed-up NFSv4 volume (/storage) - for further information about its backup policy, let us refer you to MetaCentrum site.

All the CERIT-SC computing nodes provide the following types of storage volumes, which are available for users:

• /scratch - fast filesystem (having the storage capacity of about 8 TB), dedicated for applications' temporal/working data. This volume is local on every computing node, provides a basic protection against HW failures (RAID 10) and is not backed up.
  • /scratch/<username>/job_$PBS_JOBID
  • automatically created directories dedicated for temporal/working data of the jobs; These volumes should be used only by currently running jobs, so any data must be removed immediately after a job finishes.
  • to access the volume, use the $SCRATCHDIR environment variable

If your job operates with large files, store them in the relevant subdirectory of the /scratch volume (on the machine your job really runs!). This volume is provided by high-performance local discs, and thus the delay of IO operations will be minimized.

• Shared network file system AFS on all machines

• /home directories on local cluster - This space is visible by all the nodes in the cluster. Your home directory is best for compiling and building programs and for storing output that consists of large numbers of small files. Use this volume for storing your data (storage-brno3-cerit.metacentrum.cz serves as home directory for all CERIT-SC resources.).
• /storage/home ... use this volume for data, which you want to make available from the MetaCentrum nodes, archieval storage can be used for data, which you want to make permanent and backed-up.

• /storage - MetaCentrum's shared and backed-up NFSv4 volumes (available from the frontend as well as all the computing nodes)

The structure of user home directories is as follows:

Note: The often user problem is the inability to access the folders in /storage while they are logged in to frontend by the ssh key. In this case they don't have generated the Kerberos tickets. This can be repaired by invocation of kinit command.