Re optical media decays, yes, this is<div>always a possibility. Bad batch of blanks?</div><div>There's a vast lore about what causes</div><div>CDs and DVDs to deteriorate. Whether</div><div>rewriteable media are better or worse</div>
<div>than write once, etc. </div><div><br></div><div>But there is still the issue of the original</div><div>machine being able to read them. Perhaps</div><div>that has to do with alignment issues between</div><div>DVD units. One hates to think about this,</div>
<div>but apparently it is common enough. </div><div>It somewhat says one should keep around</div><div>the very DVD unit they used to make the</div><div>backups.</div><div><br></div><div>But better is to try them right after making</div>
<div>them, one another unit if possible, which I </div><div>suspect few of us usually do.....</div><div><br></div><div>Thanks for the tip about ddrescue. I'll</div><div>take a look at it. The media in question </div>
<div>have no scratches, but there are other</div><div>possibilities. In the end I'll probably</div><div>just put the DVDs in to the old unit, read</div><div>them, move them to the new unit, and </div><div>consider it yet one more lesson learned.</div>
<div><br></div><div>Your point about several kinds of backup</div><div>is well taken. It's all a matter of how much</div><div>what you are backing up is worth to you.</div><div>And of course one always has to ask</div>
<div>whether their backup devices are working</div><div>as expected...</div><div><br></div><div> -- Bob</div><div><br></div><div><br></div><div><br></div><div><br><div class="gmail_quote">On Thu, Jan 21, 2010 at 11:16 AM, Michael Mol <span dir="ltr"><<a href="mailto:mikemol@gmail.com">mikemol@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div class="im">On 1/21/2010 10:43 AM, Bob Kline wrote:<br>
> mount /dev/dvd<br>
><br>
> That would be fine if it worked...<br>
><br>
> On occasion I'll see "no medium found<br>
> on /dev/sr0," the dvd unit. Other times<br>
> I might see "can't read superblock," or<br>
> something thereabouts. I gather that<br>
> indicates that the file system type is not<br>
> correctly determined. But if I specify it,<br>
> that should not be an issue.<br>
><br>
> Suggestions? Marginal DVD unit?<br>
<br>
</div>mount -t auto /dev/srN /mountpoint<br>
<br>
ddrescue will help you recover data from scratched discs. Optical media<br>
decays, though, so it's possible it may be totally unrecoverable. (Some<br>
brands and dye types decay faster than others. I used to know a lot<br>
about which were more reliable, but that's all pretty much slipped away.<br>
For backup purposes, don't trust just one backup medium, and keep burned<br>
discs in dark places.)<br>
<br>
Another means of backing up optical media is to use cdrdao, and rip in<br>
disc-at-once mode. I had to resort to that to back up an old Playstation<br>
disc. You should then be able to use cdrdao to burn it on to new media.<br>
I haven't dug into how to directly access the resulting .bin file, yet.<br>
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</blockquote></div><br></div>