The Exabyte tape drive is unit mua0:. A tape must be initialized upon
first use. Do not do this if there is already data on the tape, and
you wish to add new data to it ! To initialize the tape type:
where NAME is a 6 letter or less identifier for the tape. NAME is, in DEC-parlance, the LABEL of the tape. Next the tape must be mounted. Type:
$ MOUNT/FOR MUA0:Now you are ready to write a backup save set on the tape, if that is what you want to do. Just type:
$ BACKUP/LOG/VERIFY *.*;* MUA0:JUNE1594.BCKThis will save everything in the current disk directory to the save set called JUNE1594.BCK on the exabyte tape. The LOG option prints out what is happening on the terminal screen, while the VERIFY option does a check pass, comparing the file on the tape with that on the disk, after the save set is written.
After the tape is loaded into the drive, press ``load'', then
``online''. The user must mount the tape using:
(This must be done before any data can be written to tape.) If you wish to unload a tape, you can do it through the software using the VMS command:
$ DISMOUNT MSA0:
At present 3 tape formats are supported. You can tape FITS files in
either an automatic mode (i.e. at the end of each exposure) or frame
by frame. You can tape FIGARO files using the VMS utility BACKUP.
You can also tape files in the TYB tape format (for consistency with
old data analysis software packages written by Todd Boroson) either
one by one or, at the end of the night, tape every file on the disk
with the command ALLWTYB.
A 6250 bpi BACKUP tape will hold at least 192,000 blocks of data (at
least 76 800x800 integer frames).
Do not use the VMS utility BACKUP when exposures are occurring. If you
tape using BACKUP wait until the end of the night or stop observing to
write to tape.
If you type YESTAPE, the mode of operation is that a FITS file will be
written to tape after each CCD is read out (except for those exposures
taken by test words). If the tape is off line or otherwise unhappy an
error message will be typed, and the data will not be taped. (If this
occurs during a long exposure, the error message will appear in the
exposure log file; it will not appear on the terminal screen.)
YESTAPE asks for the name of the tape drive which is to be used for
output (i.e. for writing FITS files of the data) and for the tape
which is to be used for input. If you are extremely conservative, you
may wish to set the input tape drive to some non-existent unit, so
that if you by mistake type a command which reads from tape, nothing
will happen. (At present, since there is only 1 tape drive supported
via the Microvax in each telescope, the input and output tape drives
must be identical, if you wish to both read and write tapes.)
Users may want to save only their flat fielded frames, or may wish to write a VMS backup tape with FIGARO files instead of a FITS tape. (If you choose this option, you must have access to a VMS VAX on which FIGARO with a version number of 2.0 or greater is running.) If so, they should type NOTAPE to disable the automatic taping. To restart the automatic taping type YESTAPE. If you type NOTAPE, I am not responsible if you somehow manage to delete your data files. However, I expect most users, as they gain experience and confidence with OBSERVING on the Palomar Microvaxes, will operate in the NOTAPE mode.
To write a FITS file on tape from an OBSERVING disk file called
A123F.dst, type TFITS A123F. (TFITS is a modified version of the
normal FIGARO routine WIFITS which forces the creation of the proper
header data in the FITS file, and contains 16 bit data.) The standard
FIGARO word to read FITS tapes (called FITS) will read the data
correctly. It will handle the header in the way described in the
FIGARO documentation, namely the *.OBS structure will contain only the
object name, with the rest of the header loaded into the *.FITS
structure. The tape blocksize parameter (with values from 1 through
10) is supported here.
Both TFITS and the automatic writing to tape that occurs if YESTAPE is enabled check for various possible tape errors (off line, end of tape, etc). If such an error is detected during the execution of an interactive word (such as TFITS or a short exposure, for example), the terminal bell will ring about 10 times. If the end of tape (or tape offline, or other tape error) occurs in the writing associated with a long exposure which is spawned into the background mode, then an error message will appear in the job log, but not on the terminal. Thus you should watch the tape status light once in a while or look at the exposure log once in a while to see that the tape drive is functioning correctly. To see the specific error which occurred, look in the log file for the batch job (i.e., TYPE ***.LOG, where *** is the name of the spawned job.) If an end of tape error is detected, you must then remove the tape, load another one in the tape drive, mount it, and manually rewrite the frame which was being written when you wrote off the end of the tape.
FITS is the standard FIGARO word for reading FITS tapes. It has not
been modified in any way. It (and the standard FIGARO word for
writing FITS tapes, WIFITS) support the tape blocksize parameter, with
values from 1 to 10.
ALLFITS writes all frames in the current directory to tape in the FITS
format. You should first mount the tape and use TPOSITION to position
it, if it contains previously written data that you wish to save. Use
ALLFITS at the end of a night of observing if you wish to save all
your data in FITS format.
WTYB will write a single disk file to tape in Todd Boroson's tape
format. You should first mount the tape, and if the tape is partially
used, use TPOSITION to get it to the correct place to begin writing
data. WTYB will check for various tape errors in the same way as
TFITS.
ALLWTYB will write all frames in the standard CCD scratch directory to
tape in the Boroson tape format. You should first mount the tape and
use TPOSITION to position it, if it contains some previously written
data that you wish to save. Use ALLWTYB at the end of a night of
observing.
RTYB is the standard FIGARO word for reading tapes in TYB's format.
It has not been modified in any way. You can use it to check tapes
written with WTYB or ALLWTYB.
SKIP is the standard FIGARO word for skipping files on a tape. If you
answer a positive number N, the tape drive will move forward N end-of
file marks, while for a negative N, it will move backward from its
current position.
TPOSITION will properly position a tape for use in writing FITS files.
It should only be used for partially used tapes, on which you want to
continue writing after the end of existing data (as defined by a
double end of file). Don't use TPOSITION on new tapes, just MOUNT
them. TPOSITION should not be used if you are using the VMS utility
routine BACKUP -- BACKUP has its own way of accommodating this need.
BACKUP also senses the end of tape status flag.
TAPEOF will write a single end-of-file mark at the current
position of the tape drive in use. You should use this only if you
know what you are doing. Otherwise, use the standard tape writing
words supplied, i.e. TFITS, WTYB, or ALLWTYB, or the VMS utility
BACKUP.
There are several cautions I must express if you tape using the FITS
format. If you carry out data reduction to the point of generating 1d
spectra, be careful with using FITS to save the data, as FITS does not
properly deal with spectra. As far as I can see, it assumes the
spectra are linear in wavelength and only saves the two relevant
constants. This is in general a poor assumption once the spectra are
calibrated in wavelength. Unless you do not calibrate your spectra
(i.e., leave everything as a function of pixel number only) or are
more familiar with FITS, don't use it for spectra.
Another problem comes if you flat field or otherwise process your 2d images. FITS does some scaling to the maximum and minimum values in the image to fit all data into 16 bits. Thus, if you have images with values which exceed the range -32767 to +32767, the data (which lies within that range) will be crunched and resolution lost when it is written with FITS. This does not affect raw images, as all data lies within the specified range. It will not be a problem if you store flat fielded images as integers, so that under or overflows which may arise in the flat fielding are suppressed. I merely urge caution.
The tape drive controller in both of the Microvaxes is capable of
running the 1600 bpi Cypher tape drive used in the telescope control
system. There is thus at least some backup capability easily at hand
-- you just have to switch the cables from one tape transport to the
other. If you have to use this option, remember to mount your tape
1600 bpi (i.e., MOUNT/FOR/DEN=1600 MSA0:).
To provide more compact data storage for observers, Exabyte tape
cartridge drives have been installed on the MicroVAX instrument
computers at the 200- and 60-inch telescope domes. These drives use
8mm, video cartridge tapes as the magnetic media and are capable of
containing approximately 2.04 gigabytes of data on one cartridge.
Using VMS backup, one cartridge could hold at least 1590 800x800
integer frames or 240 2048x2048 integer frames.
Currently each device is configured as MUA0 and is fully compatible with all MicroVAX software that uses tapes. To write backup tapes, the mount command is MOUNT/FOR MUA0. To use the Exabyte tape with Figaro or Observing software, use the command TAPEO MUA0 to set the default tape device to MUA0.