Dear users of the SuperMUC Petaflop system at LRZ, based on user request as well as internal constraints, we intend to change the way how very large jobs (i.e. those submitted into the special job class) are processed. The new procedure for doing this is defined as follows: 1. Any user wishing to run a job in the special class must open a service request at the LRZ service desk ( https:// servicedesk.lrz.de/?service= Hochleistungsrechnen%20und%20Grid-Supercomputing%20%28SuperMUC%29& lang=en), stating (a) the job run time, (b) the number of requested nodes for a job, (c) the number of jobs with these resources. Some justification / rationale for running jobs of this size should be provided; also providing contact data (phone numbers, skype address) is considered helpful. 2. After the user s account has been validated for the special class, the user can then submit jobs into that class. All such jobs should be put into the user hold state via llhold . If there are dependencies between jobs, these must be accounted for by the submitting user (e.g. via the @dependency keyword). The submissions should be consistent with the initial specification. 3. Once a sufficient number of jobs is in the queue and the operational conditions are considered suitable, LRZ will schedule a block operation phase; this will typically last a limited amount of time (usually at most 2 days). No guarantees can be given on which of the jobs queued in special will be processed. The block operation phase is initiated by flushing the machine; this means that all running jobs will be terminated. If rerunnable, these jobs will be rerun as soon as regular operation is resumed, and no accounting is performed for terminated jobs. 4. After completion of the processing, users whose jobs ran successfully are obliged to provide feedback on the scientific and performance results of their runs (e.g. a draft paper) via the original service request. For unsuccessful runs, feedback on observed behaviours and error signatures must be provided. The next block operation has been tentatively scheduled for Monday, Jan 27, 2014, 9:00 and will terminate on Wednesday, Jan 29, 12:00 at the latest. Please submit any service requests for this block operation as soon as possible; before specifying any resources please also check with your project manager whether your processing budget is sufficient to cover the expense of CPU time required by your jobs. This information is also available on our web server http://www.lrz-muenchen.de/services/compute/supermuc/aktuell/ali4738/ Reinhold Bader