The /scratch1 or /scratch2 file systems should always be referenced using the environment variable $SCRATCH (which expands to /scratch1/scratchdirs/YourUserName or /scratch2/scratchdirs/YourUserName on Edison). The scratch file systems are available from all nodes (login, and compute nodes) and are tuned for high performance. We recommend that you run your jobs, especially data intensive ones, from the scratch file systems. The "myquota" command (with no options) will display your current usage and quota. NERSC sometimes grants temporary quota increases for legitimate purposes. To apply for such an increase, please use the Disk Quota Increase Form. The scratch file systems (/scratch1 and /scratch2) are subject to purging. Files in your$SCRATCH directory that are older than 12 weeks (defined by last access time) are removed. The /scratch3 file system is subject to purging as well, with files that haven't been accessed in 8 weeks being removed. Please make sure to back up your important files (e.g. to HPSS).