The Mark5 disk-based system has replaced the various tape based VLBI recording systems. This system is a major advance on many fronts including scheduling. To a much greater degree than with previous tape systems, schedulers can ignore the recording system other than making sure that they are not scheduling to record more data than can fit on the disk space that they have been allocated.
SCHED supports Mark5 on the VLBA by including the required commands in the telescope control files (the crd files). For systems controled by the Field System (PCFS), SCHED writes a .vex file in VEX format with the necessary commands to control Mark5. The Mark5A system is meant as a plug replacement for MarkIV or VLBA tape recorders. It still records the same tracks that would be recorded on a tape system so SCHED must still be aware of management of such issues. Such concerns will be less, or at least different, for more advanced versions of the disk based recording systems.
There are a few controls needed to schedule Mark5 natively. First, the station catalog must show that the station has a disk system. That is done with the DISK keyword. This is separate from the RECORDER keyword to allow a station entry to cover both tape and disk systems during the transition period. There is a station catalog keyword MEDIADEF that sets the default medium to use at each station. SCHED will use that default in the absence of an overriding MEDIA command in the TAPEINI section. Schedulers for most VLBA observations should probably ignore the problem and let operations deal with getting the recording system right by rerunning SCHED just before the observations. For EVN and Global sessions, it should be clear before the session which system will be used.
The examples egmk5vlba.key and egmk5vex.key show how to set up Mark5 observations. Now that the conversion to disk is complete all other examples have been, or will soon be, switched to disk.
SCHED supports VLBI over networks. This can involve real time correlation in which case the data are routed directly to the Network. An alternative might be called ftp VLBI. In this case, the data are recorded at the station, then read back through the Network, or alternatively, sent over the Network and recorded at the correlator, or both. There are a few parameters meant to help control eVLBI observation DATAPATH, GRABTO, GRABTIME, GRABGAP. This documentation needs to be updated more on how eVLBI is actually controlled. eVLBI is in regular use in Europe, but not on the VLBA, mainly because of differences in the availability of affordable network connections of adequate bandwidth.