You can backup an individual grain by clicking the download backup icon at the top of your sandstorm app. The entire sandstorm installation can be backed up safely by stopping sandstorm:
sudo service stop sandstorm
and taking a filesystem snapshot of /opt/sandstorm. If your
filesystem doesn't support online snapshots you can make a quick
backup by running:
cp -a /opt/sandstorm [the destination of your backup]
Alternatively one can make a backup using tar
tar -cf [location of tar archive] /opt/sandstorm
Then restart sandstorm to end the interruption:
sudo service start sandstorm