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: http://www.atnf.csiro.au/people/Tasso.Tzioumis/sched/TAPE_CHANGES.html
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If a project is being scheduled that uses stations that have only one tape drive, it is necessary to schedule in a gap of about 15 minutes for that tape change to be accomplished. Some stations can do it faster, but it is best not to count on it. The VLBA stations and the VLA all have 2 tape drives each and the project will switch from one to the other when the first runs out. Then the operators can change the full tape at their leisure. For these stations, it is not necessary to schedule tape change times. SCHED will complain, but not die, if a single tape station is requested to change tapes in less than 15 minutes. The SCHED input parameter TAPE is used to force tape changes. It can take station names as arguments if you only want to change tapes at a subset of stations.
An additional concern is that postpasses are needed for thin tapes. This can consume up to 22 minutes. See the beginning of this section for more details.
Sometimes it is a good idea to synchronize tape changes at at least some of the sites. For example, at least in late 1996, the VLBA correlator will not process the time between tape changes at different sites if they are less than something like 3 minutes apart. For optimized schedules, this can present a bit of a problem, so the input parameter TAPESYNC is provided to try to cause all stations that are near the end of their tape to change when the first reaches the end. With automatic tape allocation, the user does not have control of this factor and should not worry about it, although it might cause some loss of data.