There is some complexity involved and you may need to read this article twice ;-)



Mainly because of the different exceptions and the role of the software vs. hardware.

First maybe the difference between a full erase and a quick erase on drive level:

I'm intentionally mentioning drive level because in most cases it's the drive that executes a blank command sent by the software. So for the software it's more or less a "hit and run" command. Send it down and walk away or poll the drive till ready.

When a full erase command is issued on re-writable optical media then the complete surface of the disc is over-written with a neutral pattern (all zeroes or all 0xAA or something like that). The result is that all data that was once present is now gone forever. There are no magical tricks to ever find the data back, the old content has been wiped completely, not even in a high end laboratory with geniuses at work would it be possible to recover the data. Additionally, the disc's structures on the inside rings, which all drives use to determine the layout of the media , have been updated to resemble empty media. All references to tracks and session that were once there are now gone.

A quick erase is meant to be quick (duh ...) and therefore the disc's main data area is left unaffected, or at least mainly unaffected. All (or most) data remains present on the disc. What changes is the disc's structures again, on the inside rings of the media. All references to tracks and session are deleted and the media is left in a state which seems like empty media for a CD/DVD writer (in most cases ... read further).

So if the bulk of the data is still there after a quick erase ... what's the problem then you ask ?

Well, the biggest problem exists for CD-RW and DVD-RW (DVD dash / minus RW).

As I explained before, during a quick erase on drive level the disc's structures are changed so that a drive sees the disc as blank media again afterwards. And that is the big problem, an empty disc - as far as the drive is concerned - is an empty disc and the drive will not allow to read anywhere on the disc. All read commands fail immediately with drive generated errors. The drive doesn't even try reading on the requested locations. At this point the drive is the limiting factor, there is no way to circumvent this as it's not possible to tell the drive there is different media inside than what the drive sees for itself (*).

The only way (*) around this problem is to send the disc to a (possibly expensive) recovery lab that may have the right equipment to deal with it. As this is a by hardware limited problem, some labs have custom made hardware to deal with this specific problem.

(*) If I notice there is more interest in this then I will dedicate another article to this problem, in particular how a handy person with too much free time could try a few things.

There is one big exception for DVD-RW (not CD-RW) if the erase software works in the spirit of the DVD+RW standard. Meaning that the software doesn't issue a "quick erase" command but instead does the erasing by itself, like it would on DVD+RW. Read further to understand.

The big exception to all the above is DVD+RW (DVD plus RW). The designers of the format were clever enough to decide that there shouldn't be an erase function for this format at all. After all a full erase only adds to the so called DOW (Disc Over-Write) and thus reduces the quality of the media. If a full erase is truly required by the user then the application software can still simply write a neutral pattern over the complete surface of the disc with the same effect. And as a DVD+RW can have only one track in one session, changing the inner circle structures is not needed either. If there is a track already ... well then there is a track already .. why change that ? If one wants to write new content then the old data can simply be overwritten. Of course this also positively influences background format and other features I won't go in to now. In other words there is no erase command that an application can send.

If a user wants to quick erase a DVD+RW then the application software must be clever enough to simply write some neutral data over file-system structures (e.g. ISO9660 and UDF etc). And in fact that's what most applications do when they quick erase a DVD+RW.

The consequence is that for a DVD drive there still is a track after a quick erase, so this is not blank media, and if there is a track with a length then, data recovery software can send read commands and get data back. And a scan for missing data can yield to positive results.

Same as with DVD-RW there is a big exception. The reason is that in the beginning not all drive manufacturers understood the philosophy and spirit of the well thought out "no erase command" principle. So what they did was make sure that a format command basically does what an erase command did and then they informed all software vendors, which were obviously confused, that they should send a format command instead of a blank command. Wrong ...

To the best of my knowledge most drive vendors today have adopted the "no erase" +RW philosophy properly and recently developed drives don't erase anymore, even not when a format command is sent. The same goes for the software vendors, they too saw the light. However ... it's hard to change the world and exceptions still exist out there.

So when people ask, "I have a quick erased DVD+RW or DVD-RW ... can it still be recovered", it's difficult to give a definitive answer because it depends so much on the type and make and even firmware revision of the writer, in combination with the erase software and version of that software.

From experience, quick erased DVD+RW media, erased with a current drive and current software is very often recoverable. Chances for success degrade significantly for DVD-RW, because many applications simply send an erase command (or format command) to the drive. Quick erased CD-RW is only recoverable in the lab or with special tricks that are hard to explain here.

Hope this made sense to you ...

Terminology:

"Erase" and "Blank" are basically the same, software mostly uses the term "Erase" whereas official specifications and standards use the term "Blank", as in Full Blank or Quick Blank.

Interesting links from wikipedia explaining the different formats:

http://en.wikipedia.org/wiki/Compact_disk_erasable

http://en.wikipedia.org/wiki/DVD-RW

http://en.wikipedia.org/wiki/DVD_plus_RW

http://en.wikipedia.org/wiki/DVD-RAM