Whipple Data Archiving Using DVD-RAM
The Whipple Observatory's
10 m gamma-ray telescope generates roughly 1 GB of data in a
single night's observation. These data are archived locally and
distributed to several institutions world wide for subsequent
reduction and analysis. In the past we archived data on 4mm digital
audio tapes (DAT) and compact disks (CDROM). DATs though high in
capacity (2 GB per tape), are limited to sequential access and
therefore quite slow. In contrast, CDROMs provide random access so
are much faster but are limited to 650 MB per volume.
DVD
The next generation of optical
digital data storage is the digital verstile disk (DVD). As this
technology is new, a standard format is yet to emerge. In the mean
time, several groups of electronics manufactures have developed their
own format in the hope that their hardware becomes the standard. Thus
far DVD-R, DVD-RW, DVD+RW, DVD-ROM and DVD-RAM have been
introduced. Information about the various formats can be found in the
DVD FAQ and a
good article about writeable DVD by E-Media
Professional.
DVD-RAM
We decided to go with DVD-RAM because
of its large capacity, 5.2 GB on double sided disks (9.4 GB disks are
now available) and its re-writable capability. DVD-RAM drives are made
by Toshiba, Hitachi, Panasonic and Pinnacle Micro. We purchased the
Panasonic LF-D100.
Using DVD-RAM with Linux
The Linux kernel recognizes
the Panasonic LF-D100 drive as a read only CDROM device. Your first
step will be to patch the kernel to recognize the drive as both CDROM
and Magneto Optical device.
- Patch the Linux kernel SCSI driver (scsi.c)
- original
patch for kernel 2.0.33 by Nagai Hidetoshi
- patch ported to kernel version 2.2.1
Next if you are using a kernel version prior to 2.1.32 you will
also have to apply a patch to the scsi drive device (sd.c) to support
2048 bytes/sector drives.
Now you should be ready to use your DVD-RAM drive.
The DVD-RAM drive will be recognized by kernel as two devices
- Magneto Optical Drive - /dev/sdx - where x is the drive identifier
starting from a and goes in order of scsi id number.
- CD-ROM Drive - /dev/scdx - where x is the drive identifier
starting from 0 and goes in order of scsi id number
The optical device may be treated as a removal disk.
- do not partition the disk, simply write a filesystem to the entire
disk, for example - mke2fs -b 2048 /dev/sdx
- mount disk - mount -t ext2 /dev/sdx /mnt/dvd
(assuming the directory /mnt/dvd already exists)
- simply copy data to it - cp -a /data/* /mnt/dvd
We have successfully archived data to DVD-RAM using a Compaq Alpha
running RedHat Linux 6.0.
Universal Disk Format (UDF) - standard DVD filesystems
In order to be able to read a DVD disk on any platform a
standard filesystem has been developed called
UDF. This performs
a function similar to the ISO9660 filesystem structure developed
for CDROM technology. I have not yet tried writing a UDF filesystem
to DVD-RAM but do not see why dd shouldn't work.
lessard@physics.purdue.edu