From PatrikR's VXA link:
VXA is the only tape format in the world to write and read data on tapes in individually addressed data Packets.
I have to say that I am absolutely dumbfounded to read that.
Let me tell you a story that I thought was ancient history:
Many years ago I had a QIC tape backup system from Emerald Systems. To give some idea of the timeframe, the tapes each held 60 megabytes. I used their tape system to back up the development files of my company.
One day while editing a file, I happened to destroy it. So, I went to the most recent backup tape to attempt to recover a recent version of the file.
A short way into reading the backup tape, the drive reported an unrecoverable read error.
At which time it stopped.
It didn't continue reading past said read error, which was on a part of the tape that didn't contain my lost file. It simply stopped, and refused to read anything at all past that first error on the tape.
After some angry calls to Emerald Systems, I was told that the design of the QIC tape standard was such that drives couldn't read past an error.
Frankly, I thought that I was being fed a line of BS, and never again did any business with Emerald Systems.
As an engineer in the microelectronics field, I am absolutely dumbfounded to read that not only was what Emerald said about QIC tapes apparently true, but that this design flaw has continued to exist in the multiplicity of tape standards that have been developed since that time. It seems to me to be utterly obvious that a backup tape system has to be able to ignore bad spots on the tape and recover all the readable data that is beyond the bad spot. How this situation could have been designed in in the first place, and then continued to exist for these many years, is stupidity of a level that exceeds my ability to comprehend.
Reviewing what I just wrote, I see that it was quite a rant! I guess the loss of that data after having spent thousands of dollars on a backup system that didn't work still stings. I guess the moral of this story is not to trust your precious data to backup tapes that can't be read if there are any bad spots. Which would appear to imply that VXA tapes are the only tapes which might be suitable.