One of the most frustrating things that can happen in a backup operation (or worse yet, during a restore) is for the tape library to fail to read the bar code label identifying a tape cartridge. The result can be anything from a lot of manual fiddling to a discarded tape cartridge. In general, the best thing to do is to discard a cartridge the first time the drive or library fails to read it -- after recovering the information on the tape, if necessary. Fortunately there are a number of steps you can take to prevent problems.
Modern tape drives and libraries are remarkable finicky about the labels. If the there is not a clear, high-contrast distinction between the white and black bars in the bar code, the device may read the label erratically, or more likely fail to read it at all. This can be true even if another device of the same make and model can successfully read the label. The relevant ANSI specification, X3.182, lays out in considerable detail how a bar code must appear to the reader. It also establishes quality levels for bar codes. In general backup tape equipment expects labels meeting the highest, grade A, quality standard.
The reason this causes so much trouble in data centers is that the typical computer printer cannot consistently produce labels of this quality and trying to do so give inconsistent results. Hewlett Packard, along with many other makers of tape drives and cartridges, recommends using pre- printed labels from approved suppliers as a way to avoid trouble.
Print quality aside, HP says there are other things which can cause problems with cartridge labels. For example some libraries have problems with DLT cartridges with more than 7 characters because of the density of bars and spaces. Likewise, HP says, some libraries have trouble with LTO tape labels containing more or less than 8 characters. Another problem with LTO labels, according to HP, is that HP LTO libraries expect two lines of bar code instead of the HP-specified dual line bar code.
HP discusses labeling issues in a white paper titled "HP Bar Code Label Requirements, Compatibility and Use" available at: http://www.hp.com/products1/storage/products/storagemedia/WP_barcode.pdf
For more information:TIP: Be careful with tape labels
Related links: Automated tape libraries
Related links: Backup/Archive
About the author: Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.