Managing the use of tapes, Cleaning tape heads

NOTE: Using immediate mode with other commands does not improve performance and can cause problems when writing a driver. The SCSI specification requires that if a command is issued with the IMMEDIATE bit set to 0, the drive must flush its data buffer before it carries out the operation. This takes time.

Managing the use of tapes

The Ultrium format enables applications to monitor the performance of tapes closely, to indicate when tape heads need cleaning, and when a tape should be discarded.

See “Use of tapes” on page 19 for more information.

Information in Cartridge Memory

The LTO Cartridge Memory holds a number of pages of information that contain data about the tape’s history, such as the amount of data written to and read from the tape, the number of times a cartridge has been loaded and the tape threaded into a drive, and the number of read or write errors that have been encountered by drives with this tape. This information can be used to warn against backing up onto a tape of dubious quality, or one that is reaching the end of its life.

Cleaning tape heads

The ‘Clean’ LED on the front of HP Ultrium drives indicates when a cleaning cartridge should be used. There are two ways for backup applications to determine when the tape heads need cleaning and to prompt the user to clean the drive:

•Use TapeAlert—see“Monitoring the condition of the drive and media” on page 78 for details.

•Send a SCSI REQUEST SENSE command to look at the CLN bit in the sense data. If the bit is set, the drive needs cleaning.

In an automation context, the tape drive tells the automation controller that a cleaning tape needs to be used through two bits in the ACI Get Drive Status command.

•The Cleaning Needed bit signals deterioration in the write or read margin of the drive and indicates that a cleaning cartridge should be used as soon as possible. Once the drive has been cleaned successfully, the Cleaning Needed bit will be cleared.

•The Cleaning Required bit indicates that the drive is unable to read or write unless the drive is first cleaned, so a cleaning cartridge should be used immediately. Following a successful clean, the Cleaning Required bit will be cleared.

Monitoring tape use

Drives can report the actual amount of data that has been written to the tape, and the amount of available space on the tape. From this information, applications for Ultrium drives can be designed to calculate the percentage of tape used, and give the user feedback on the actual progress of the backup operation. This is a significant improvement over other technologies, such as DC6000 QIC products, that require the application to estimate what is going on.

12 Designing backup applications

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