# Global common¶

The global common file system is a global file system available on all NERSC computational systems. It offers a performant platform to install software stacks and compile code. Directories are provided by default to every MPP project. Additional global common directories can be provided upon request.

space quota inode quota purge time backups
10 GB 1 M none yes

Your groups usage can be viewed with the cmnquota <proj_name> command.

## Usage¶

Global common directories are created in /global/common/software. The name of a "default" project directory is the same as its associated MPP repository. There is also a Unix group with the same name; all members of the repository are also members of the group. Access to the global common directory is controlled by membership in this group. Because this directory is shared across all systems, you may want to install your software stacks into separate subdirectories depending on the system or the processing architecture. For some general programs you can use the same installs across all systems, but for best performance, we recommend separate installs for each system and architecture (e.g. for edison vs. for Cori KNL).

Warning

Global common is mounted read-only on the computes to improve performance. Software installs should be done on the login nodes.

## Performance¶

The global common system is optimized for software installation. It has a smaller block size and is mounted read-only on the computes. This allows us to turn on client-side caching which dramatically increases the read time of shared libraries across many nodes. The cache expires after five minutes, so it is not recommended you compute against code that is being actively (i.e. within five minutes) changed.

## Backup/Restore¶

Warning

No managed backups of global common directories are done by NERSC.