Using DVDs with AIPS

Astronomical Image Processing System

Greg Taylor and Eric W. Greisen
Last update: November 11, 2004

Using DVDs with AIPS

We describe three ways to use DVDs for the storage of AIPS data. The benefits and limitations of each should be considered before making the choice of format. On this page we describe the various options and provide more detailed information. For a description of the various DVD types (DVD+R, -R, +RW, -RW, -RAM) see the DVD FAQ.

(1) DVD as a re-writable AIPS drive

With DVD+RW disks and the UDF (Universal Disk Format) it is possible to create an AIPS drive that uses a DVD in the same way as a regular hard drive, with the benefits that it can be removed and shared. There are some limitations, however, in that DVD+RW drives are at least 5 times slower than a typical hard drive, and they are rated at only 1000 writes. This means that active data reduction using a DVD+RW drive would be impractiably slow and eventually lead to corruption of data. Copying data over, and deleting unwanted files, should not pose a problem. To increase lifetime, UDF disks can be mounted read-only when the intention is only to read them.

One other caveat to this process is that the user must realize that in storing the raw AIPS data, the byte order will be set by the operating system (Little Endian vs Big Endian), so that DVDs written on a Linux machine (Little Endian) will not be readable on a Sun or MacIntosh (Big Endian), even if the DVD can be mounted and all the files seem to be in place.;

For more information about creating r-writable DVDs see the AIPS Memo. Some caveats about this process were discussed in the 31DEC04 (30Jun04 AIPSLetter) on pages 3 and 4. For details on overcoming these caveats, namely about what it takes to get the UDF installed on a Linux machine, see Tracey Delaney's notes on installing UDF.

(2) DVD as write-once AIPS drive

If UDF is not supported at your site or machine, but you have a DVD burner available, then all is not lost. For any AIPS area up to 4.7 GB in size it is fairly straightforward to make a copy of that area onto a DVD that can then be removed and shared. This is a write-once operation, and the data cannot be subsequently modified, even if the DVD is a +RW or -RW type (without erasing the disk completely). However the disk so created can be written on any type of DVD, and read by nearly all operating systems.

The ISO 9660 file format is more primitive than UDF but has been in use for many years and is the format for most CDs. There is a suite of utilities called dvd+rw-tools installed on most Linux boxes. On a Mac OS X machine one can use the built in burner. First create an AIPS DISK area on a hard drive in the standard fashion (and edit AIPS_ROOT/DA00 files DADEVS.LIST and NETSP). Writing of these disks is typically done in a single session. For example:

  % dvd+rw-format /dev/dvd  ! not necessary for DVD+R or DVD-R disks
  % growisofs -Z /dev/dvd -R -J /some/aips/directory/
  % mount /mnt/dvd
  % ls /mnt/dvd             ! to see that its all there
  % ummount /mnt/dvd

Next, create a symbolic link that points to /mnt/dvd and edit AIPS_ROOT/DA00 files DADEVS.LIST and NETSP to include it in the listed AIPS data areas.

To fill an entire disk should not take longer than 30 minutes (at 2X), and for DVD+-R should be done in under 16 minutes (burning at 4X).

A caveat to this process, as with UDF DVDs, is that the user must realize that in storing the raw AIPS data, the byte order will be set by the operating system (Little Endian vs Big Endian), so that DVDs written on a Linux machine (Little Endian) will not be readable on a Sun or MacIntosh (Big Endian), even if the DVD can be mounted and all the files seem to be in place.

(3) FITS files stored on a DVD

If all you want is to archive your AIPS data to DVD, then consider writing out the data to a disk area in FITS format. This area can then be written to DVD in either UDF or ISO format as described in the two sections above. This data will not suffer from the byte-order problem, but to access it you will have to read it back into AIPS. There are some useful utilities in AIPS to write out all files on a given disk. First RUN WRTPROCS. Then write out the desired files with WRTDISK. To read them back use READISK.

Last modified on 2004/11/11 by Eric Greisen