The machines that have exabyte drives are s0, s1, s2, t1, and 4m. In general, these devices have been very unreliable. In IRAF the device name is mtx. Problems with computer hardware and the exabyte driver prohibits the use of the IRAF fits read and write tasks on some computers. The possible combinations are as follows:

      \fIMachine	CTIO-name	rfits	wfits\fR
      sun4/60	s0,t1		works	fails
      sun4/370	s1,s2,4m	works	works

      sun4/280			fails	works
      sun4/470			fails	works
      sun4/490			fails	works

Although this problem may be fixed by the IRAF group, people have been known to overwrite their first nights data with the second nights, thus lossing the first full nights data. BE SURE YOU MAKE BACKUP TAPES OF YOUR DATA SO YOU DO NOT LOSE ANYTHING! If you use the 4m SUN to write fits files, be warned that you should confirm the images are written on the tape. Also, you need not move to the end of the tape before continuing to write fits images on the tape. This is done by setting the newtape parameter to "no". You should not have to keep track of the number of files you have written to tape. If your machine at home is in the wrong category such that you cannot read the tapes then you should use "tar". NOTE: The newer the exabyte drive, the more reliable is seems to be. Tapes written on older devices are not compatable with the newer drives, and vice versa. We are presently in the process of updating all of our older drives with newer ones. New drives are connected at ctios2, and ctio4m.

The UNIX tar command is the best method for writing to exabyte tapes, since it is more universally used. The UNIX device name on all these machines is /dev/rst1. Putting an "n" in front of the device name means that it will not rewind the tape after performing an operation, so if you are writing more than one file to exabyte, use /dev/nrst1. There are two methods for writing to tapes. The suggested procedure for writing an exabyte tape is to first wfits all iraf images into one directory. Once all the images to be backed up are in the same place, then use tar:

      !tar cvf /dev/rst1 .

NOTE: If you specify the full path name including the disk name, you will have trouble reading the files back off at your home institution. Go directly into the directory being backed up and the path name will not prefix all your files saved to tape. To read the tape, simply change the "c" to an "x" for extract. Then rfits must be run on the IRAF images to restore them to separate header and pixel files. To list the contents of the tape, change the "c" to a "t". It is a good idea to write magtapes to backup your images before writing to exabyte tape in case files are corrupted by writing to exabyte.

If you don't have enough room on disk to fit all your images on at one time, it would be better to write each nights data separately. This has been simplified by a special task written here at CTIO. These tasks are available only here at CTIO, on the machine w1 downtown and 4m on the mountain. To use this command you must first define the tasks in IRAF and allocate the exabyte tape drive:

      set source="/uw10/steve/source/xsource/"    (DOWNTOWN)
		      or
      set source="/u4m0/steve/source/"            (TOLOLO)
      task wrk=source$work/wrk.cl
      wrk
      alloc mtx

Typing "wrk" will result in the prompt for the machine name on which you are using the exabyte, you must be remotely logged onto the machine which has the exabyte you are using. Now the package is loaded with the tasks "archive" and "restore". The task "archive" is for writing multiple tar files onto the end of a tape. Write each nights data separately making sure you specify "no" for the newtape option and the end of the tape will be found before writing begins on the second file. This can also be done by writing the header and pixel files separately, however, this will cause problems later since the header file has a path name for the pixel files. The header parameter pixfile would have to be edited using the task "hedit" when the files are read onto your system at home so that this pointer specifies the correct directory path. To do this write the main visitor directory with all the header files using the task "archive" and then move to the pixel directory using "cd imdir" and use "archive" again. To read a specific file, just use the task "restore" to restore a directory or entire file. You can use the UNIX tar command to read the file also. To read the second file on a tape using UNIX, we must advance the tape beyond the end of file marker of the first file. The tape can be advanced beyond the end of file marker using:

      mt -f /dev/nrst1 fsf

To rewind the tape, replace the "fsf" in the command with "rewind". Another way to read beyond the first file is to use "/dev/nrst1" as the device name (add an "n" in front of the original name), and to read the first file use:

      tar xvf /dev/nrst1

Then type it again, this will skip over the end of file marker of the first file. You may get an error or warning message. Now typing it again the next file will be read. So you type the command three times in a row. You must type the command 5 times in a row to read the 3rd file. The first 4 commands, a "t" can be substituted for the "x" to simply list the first two files. Tapes are available on the mountain and downtown from Mario Hamuy or Lisa Wells and will be charged to your account when you leave.