Hi! Arno Lehmann wrote: >> Test to demonstrate the random WRITE access of the media (expected on >> DVD+RW and DVD-RAM, unexpected otherwise) >> goldstein# dd if=/dev/urandom bs=1k count=1 of=/dev/cd0d seek=100000 >> 1+0 records in >> 1+0 records out >> 1024 bytes transferred in 3.046 secs (336 bytes/sec) >> goldstein# dd if=/dev/cd0d bs=1k skip=100000 count=1 | hexdump -C >> 00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >> |................| >> * >> 00000400 >> 1+0 records in >> 1+0 records out >> 1024 bytes transferred in 0.001 secs (1024000 bytes/sec) >> > > This one demonstrates that either your /dev/urandom is broken, or it's > not that simple writing raw data to and reading it from a DVD. > > Arno >
Let me redo it, I pasted the wrong line by accident. Create a file I can count as reference for comparisons goldstein# dd if=/dev/urandom of=1mrandom bs=1k count=1024 1024+0 records in 1024+0 records out 1048576 bytes transferred in 0.624 secs (1680410 bytes/sec) Write it to the DVD+RW, seek=100MB goldstein# dd if=1mrandom of=/dev/cd0d bs=1m seek=100 1+0 records in 1+0 records out 1048576 bytes transferred in 0.517 secs (2028193 bytes/sec) Read from the DVD+RW, skip=100MB (same chunk) into "1mrandom2" for comparison goldstein# dd if=/dev/cd0d bs=1m skip=100 count=1 of=1mrandom2 1+0 records in 1+0 records out 1048576 bytes transferred in 0.732 secs (1432480 bytes/sec) Read from the DVD+RW, skip=99MB (chunk just before the one I wrote) into "1mrandom3" for comparison goldstein# dd if=/dev/cd0d bs=1m skip=99 count=1 of=1mrandom3 1+0 records in 1+0 records out 1048576 bytes transferred in 1.476 secs (710417 bytes/sec) 1mrandom1 should match 1mrandom2, but not 1mrandom3: goldstein# diff ./1mrandom ./1mrandom2 goldstein# diff ./1mrandom ./1mrandom3 Binary files ./1mrandom and ./1mrandom3 differ My /dev/urandom is not much borked, as you can see here: :) goldstein# hexdump -C ./1mrandom | head -1 00000000 78 90 aa dc 4f 33 c1 22 26 71 5e f8 f9 dc fc 25 |x...O3."&q^....%| goldstein# hexdump -C ./1mrandom | tail -2 000ffff0 0f 2a a2 3e ad 6b 4a e4 ee 33 44 2a 8d b1 85 e4 |.*.>.kJ..3D*....| 00100000 goldstein# goldstein# ent 1mrandom Entropy = 7.999786 bits per byte. <<--- OK Optimum compression would reduce the size of this 1048576 byte file by 0 percent. <<--- OK Chi square distribution for 1048576 samples is 311.30, and randomly would exceed this value 0.92 percent of the times. <<--- OK, not _THAT_ good in this sample Arithmetic mean value of data bytes is 127.5141 (127.5 = random). <<--- OK Monte Carlo value for Pi is 3.140522539 (error 0.03 percent). <<--- OK Serial correlation coefficient is -0.000546 (totally uncorrelated = 0.0). <<--- OK I was not able to go to the store shop for blank media today, but will do soon. My guess is that you get "random" values, as some DVD+RW media come "preformatted", and DVD+RW features "background formatting", as I quote from the DVD+RW alliance at http://www.dvdrw.com/why/faq.htm *Can I use a DVD+RW disc to directly store my data files, or do I always need to use a burning program?* DVD+RW is the only rewritable DVD format that supports the Mt. Rainier or EasyWrite system. With an EasyWrite enabled DVD+RW drive and by using the forthcoming version of Microsoft Windows, Longhorn, you can directly store your data on a DVD+RW disc. Just as you would using a floppy diskette, although a DVD+RW offers you about 3,000 times the storage capacity! Mt. Rainier performs important tasks in hardware instead of software (like background formatting and handling of defect management) resulting in a very robust system. Also refer to glossary: Mt. Rainier <http://www.dvdrw.com/why/glossary.htm#mtrainier> And from their glossary page: *Mount Rainier (MRW)* Mount Rainier is an optional feature of the DVD+RW format, that allows for DVD+RW media to be used in a "hard disk-like" fashion on drives supporting this functionality. The drive will be accessible for reading and writing directly from the operating system and all applications without the need for dedicated recording-software. /<omitted windows-related content> / DVD-RAM also supports such "hard disk-like" functionality, although it is completely different media. I will order some blank DVD-RAM on the net, since there are no suppliers in town, and mine were already used enough. Regards Evaldo ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users
