New Procedure for writing data onto CD-ROMs at WIYN:

There has been a number of different strategies to make the process of writing CD's more robust, none of them have proven to be 99% reliable.  Our latest improvement has been to incorporate a CD writer that has burnproof technology.  This enhancement significantly reduces the number of failed CD write attempts.  In particular, it prevents the "buffer under-run"  error that has been common in our past experience.  At present, I have been able to write numerous, full CD's at 12x with no failures.  This test was with Mini Mosaic files, heavy SCSI activity, and while acquiring a series of Mini Mosaic bias images.  The test used Kodak CD-R Ultima media that was certified for 8x writing.

You may still encounter a failed CD write.  It will happen, but does not necessarily suggest that there is a component failure, or that this process does not work.  If you write enough CD's, you will almost certainly encounter a failed write, no matter the system.  Keep in mind the following, possible causes for a failed CD write:

  • Low quality CD-R media.  Try to buy media that is archival quality and tested for 12x speed write.  Most high quality (archival) media (Kodak's Ultima line) may report a write speed of 8x, but will function just fine at 12x.
  • SCSI controller activity.  We have seen in our testing that on occasion, the SCSI controller cannot perform the initial setup of the CD writer.  Try again making sure you have a good CD, mounted properly.  If you have two failures with the same, blank CD, discard it!  Start again using a new, blank CD.
  • Buffer Under-run.  CD writers are subject to writing data faster than data can be down loaded to the the writer's buffer.  This can happen if there is heavy traffic on the SCSI or IDE controllers (lots of read/write to disks, ftp, or very intensive CPU activity).
  • Verify that you have viable data files.  Be sure that you have copied to the staging directory, the files you intended, and that they are all present and viable.  If you overfill one of the staging directories, you will create multiple files with partial or no content.

CD Write Procedure

1) Convert your data to the format you wish to store on CD-ROM.
We recommend FITS. If you are storing raw data then each pixel is represented by an unsigned 16 bit short number. These data can be efficiently stored in FITS format with the following command:
cl> wfits iraf_file fits_file bitpix=16

If you are storing reduced data then each pixel is represented by a 32 bit floating point number. These data should be stored in FITS format with the following command:

cl> wfits iraf_file fits_file bitpix=-32

Note the "-" sign and note that explicitly employing "bitpix=-32" is not usually necessary as the default (bitpix=0) will select bitpix=-32 for data stored as 32 bit floating point numbers. If you are writing both raw and reduced data this additional statement would be a good idea to avoid accidentally writing reduced data with bitpix=16.

To verify your CD's at WIYN

1.) Insert CD into the CDReader on SAND below the CDWriter.  It is the ASUS 50x device.

2.) In an IRAF window, cd to the /mnt/cdrom directory.

3.) List the directory. You should get a listing of the CD top level directory. This will establish that the file system is indeed present.

Updated 02/2002
Charles Corson

Last update 02/2005