When read by the bar code reader of the library, the bar code identifies the volume label of the cartridge to the tape library. The bar code volume label also indicates to the library whether the cartridge is a data, cleaning, or diagnostic cartridge. 

Tape cartridges are often supplied with the labels already attached, or labels can be attached after purchase. The Ultrium cartridge features a recessed area for the label (see Figure 2-5 on page 53). The label must be applied only in the recessed label area. If the label extends outside of the recessed label area, it can cause loading problems in the drive. 

## Volume label format 

The LTO cartridge label uses the Uniform Symbol Specification-39 bar code symbols. 

The volume label of a cartridge consists of six characters, starting from the left. Except for cleaning and diagnostic cartridges, these six characters are limited to the following ASCII characters: 

GLYPH<SM590000> Uppercase A - Z (ASCII character code: 41h - 5Ah) 

GLYPH<SM590000> 0 - 9 (ASCII character code: 30h - 39h) 

The volume label must consist of six, all uppercase alphabetic, all numeric, or alphanumeric characters, such as ABCGVE, 123621, or F8H5N9. The volume label cannot consist of fewer than six characters. 

A volume label format of CLN Unn  represents a universal cleaning cartridge. A volume label of the form CLN vnn  is used for a unique cleaning cartridge, where v is an alphanumeric identifier that represents the vendor of a drive-unique cleaning cartridge. An IBM-unique cleaner cartridge uses the label format CLN Inn . This identifier is logged in the vendor information pages in the Ultrium tape drive. 

A volume label of the form DG(space) vnn is used for diagnostic and service cartridges. The drive uses the v to determine whether the drive-unique diagnostic cartridge is loaded. The nn represents a specific cartridge and is logged in the vendor information pages in the Ultrium tape drive. 

The internal and external labels on a cartridge do not need to match. Therefore, the volume label on the bar code label does not need to match the volume label that is recorded on the tape in the tape label area when it is initialized. However, it is preferable for them to match to avoid confusion. 

## Ordering bar code labels 

For more information about ordering bar code labels, see Appendix B, “IBM LTO Ultrium and 3592 media” on page 469. 

## Write-protect switch 

The write-protect switch is at the front of the cartridge to the left of the bar code label (see Figure 2-5 on page 53). The position of the write-protect switch on the tape cartridge determines whether the tape can be written to. The tape cannot be written to when the switch is pushed to the right. When the write-protect switch is set to inhibit writing, a visual lock mark (such as a padlock) is visible. 

In most cases, back up and recovery host application software is used to achieve the most benefit from the use of an LTO system. It is better to rely on the host application software to write-protect the cartridges rather than to manually set the write-protect switch. This way, the host software can identify a cartridge that no longer contains current data and is eligible to become a scratch cartridge. If the switch is set and the host application sets the cartridge to scratch status, the tape drive is unable to write new data to the tape. 

