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Tape Initialization File

The tape initialization file is mostly obsolete. It is possible that the ability to select the media type for particular stations will be of use in the future during transitions between recording systems. But all tape positioning capabilities became obsolete along with the tape systems. The highly unlikely that a tape initialization section is needed in any schedule file. If one is present, it is probably an artifact of the use of old templates and it should be removed.

The tape initialization information can be used to select what type of recording to make at a station and to give details about the tape recordings if tape is used.

During the transition to Mark5, there was a period where both tape and disk systems will be available at stations. SCHED needs a way to select which to use. For each station, a default can be set with MEDIADEF in the station catalog. To override that default, the MEDIA parameter is provided here to tell SCHED whether to assume that the data transmission system is specified by RECORDER or DISK in the station catalog.

The following is retain for historical reasons and should not concern most users.

If you are not using the MEDIA parameter, then you almost certainly should not be using a tape initialization section TAPEINI or tape initialization file. All the parameters have good defaults for nearly all cases so explicitly setting them is more likely to get you into trouble than to help. The capability provided by the file is only retained for special test observations. Even the MEDIA parameter is not normally needed. If your SCHED input file contains a TAPEINI section, you are probably an old time VLBI observer using ancient templates.

When using a tape system, the tape initialization information tells SCHED details about the tapes to be used at each site. In nearly all cases, the defaults are appropriate and very few users need to specify any of this information. Other than for test observations which the user may wish to start in the middle of a tape, the only exceptions are for observations that use thick tapes on Mark III or Mark IV systems. But since such tapes are no longer allowed at most stations, this should be very rare. If tape initialization information is needed, the information can be specified in an external file, the TAPEFILE, or can be imbedded in the main file following the parameter TAPEINI.

The capability to have a separate TAPEFILE was originally part of an attempt to deal with the general case of VLBA tape handling. Such a file could have been used to schedule multiple projects per tape by specifying where each project starts. The file would have one full set of inputs per project. But the automatic tape allocation by the on-line system now deals with this situation in a cleaner manner. Automatic tape allocation and automatic reversals can be requested using SCHED's AUTOTAPE parameter; however, these options only apply to sites with VLBA control systems and more than one tape drive and can only be used for projects to be correlated on the VLBA correlator. When automatic tape handling is requested, SCHED puts the appropriate commands in the control files. It also attempts to predict what the tapes will do assuming that they start in the place specified in the tape initialization file. Users should be aware that these predictions may be not be accurate because tape lengths can vary and the tape start position may depend on the preceeding project.

Note that the number of heads in use at a time (8, 16, or 32), which determines the number of passes per head index position (1, 2, or 4 as specified by TPMODE in the setup file, is not allowed to change during a project at a station, although different stations may use different values for TPMODE. This restriction avoids a the bookkeeping nightmare raised by the more general case. SCHED checks all the requested setups for a station and remembers the largest number of heads (smallest TPMODE) and allocates tape for all scans as if that value were in use. This is wasteful of tape, but allows some tests to be done with mode switching.

The following are some capabilities supported through the tape initilization file:

  1. Different tape lengths at different stations.

  2. Different bit densities, and hence tape speeds, at different stations.

  3. Tape drive and index position at program start specified for each station.

  4. Tape speed, bandwidth, and sample rate can change during run. Beware of operational restrictions on the use of this capability. See the guidelines for preparing observing schedules available from the NRAO WWW home page under VLBA.

  5. Different number of tape drives at each station.

A single set of tape initialization conditions can be specified in the SCHED keyin file using TAPEINI followed by a ``/'', in much the same way that in-line catalogs are given. This is the normal way that the tape initialization information is provided. Unlike the source and station catalogs, only one input group will be read and that group will be terminated by a ``/''. No ENDCAT or equivalent is required, or even allowed.

The input parameters of the TAPEFILE are:

MEDIA:    Which record system to use.
NDRIVES:  Number of drives at the site.
NHEADPOS: Number of head positions in use at site.
OBSCODE:  Experiment code for this observation.
TPSTA:    Station name for this group of parameters.
TPDRIVE:  The drive to begin the observation on.
TPINDEX:  The tape index at which to start the observations.
TPLENGTH: The length of the tapes to be used at the site.
DENSITY:  Are tapes at sites high or low density.
TPTIME:   Mark II tape length in time.
HEADMODE: Indicator of head positions to use.

The first example shows a tapeini section that might be used during the transition to MARK5. Note that BOTH means create a schedule with both types of control information so that operations can pick which to use. This works for the VLBA, but not for stations controlled by the VEX file. For this example, all tape parameter will take their default values.

tapeini /
tpsta    = vlba_sc, vlba_hn, vlba_nl, vlba_fd, vlba_la, vlba_pt,
           vlba_kp, vlba_ov, vlba_br, vlba_mk, gb_vlba, medicina,
           noto,    onsala60
MEDIA    = TAPE,    TAPE,    TAPE,    DISK,    DISK,    DISK,
           DISK,    TAPE,    DISK,    TAPE,    TAPE,    DISK,
           TAPE,    DISK

The second example of a tape initialization group shows the usage for specifying the tape system. Note the NDRIVES is not given so that it is picked up from the station catalog. Note that the example file for VLBI at the VLA contains a tape initialization group to show what it is like. Usually it should be reasonable to take the defaults.

obscode ='default'
tpsta   ='vlba', 'vla1', 'vla27', 'eb_vlba', 'gb_vlba', 'default'
tpdrive =1,      1,      1,       1,         1,         1
tpindex =1,      1,      1,       1,         1,         1
tplength=17600,  17600,  17600,   17600,     17600,     8800
nheadpos=14,     14,     14,      14,        14,        14
density =H,      H,      H,       H,         H,         L

next up previous contents
Next: Details of Tape Initialization Up: THE SCHED INPUT FILES Previous: Station Catalog and Locations   Contents
Craig Walker 2014-04-14