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. 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: 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. For more information about ordering bar code labels, see Appendix B, “IBM LTO Ultrium and  3592 media” on page 469. 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. 58  IBM Tape Library Guide for Open Systems Write-protect switch Ordering bar code labels Volume label format GLYPH<SM590000> Uppercase A - Z (ASCII character code: 41h - 5Ah) GLYPH<SM590000> 0 - 9 (ASCII character code: 30h - 39h)