For most VLBI observations, the data are recorded at the stations and played back later at the correlator. It is not yet possible for the recording process to be totally transparent to the user, but dealing with it is now much less of a burden than it was in the tape era. A top level issue is that a user is typically allocated a total amount of recording media that he/she is allowed to use. This number may be less than the total that could be recorded during the observation. It is required because the overall media supply may not be large enough to allow full time recording at the maximum bit rate and the scheduling committees need to apportion the resources according to the project needs and priorities.
Beyond the overall amount of data recorded, the disk-based systems still require the user to pay attention to the need for data quality checks, to maximum reasonable recording scan lengths, to the need for time at non-VLBA stations for module swaps, and to dealing with the fact that the correlatable data is not provided starting at the exact time specified for starting the recording. These topics are discussed in the Observing Strategy and Scan Times section and will not be discussed in detail here.