How NetBackup TapeAlert works
To understand drive-cleaning TapeAlert, it is important to understand the TapeAlert interface to a drive. The TapeAlert interface to a tape drive is by means of the SCSI bus. The interface is based on a Log Sense page, which contains 64 alert flags. The conditions that cause a flag to be set and cleared are device-specific and device-vendor specific.
The configuration of the Log Sense page is by means of a Mode Select page. The Mode Sense/Select configuration of the TapeAlert interface is compatible with the SMART diagnostic standard for disk drives.
NetBackup reads the TapeAlert Log Sense page at the beginning and end of a write or read job. TapeAlert flags 20 to 25 are used for cleaning management, although some drive vendors' implementations vary. NetBackup uses TapeAlert flag 20 (Clean Now) and TapeAlert flag 21 (Clean Periodic) to determine when to clean a drive.
When NetBackup selects a drive for a backup, bptm reviews the Log Sense page for status. If one of the clean flags is set, the drive is cleaned before the job starts. If a backup is in progress and a clean flag is set, the flag is not read until a tape is dismounted from the drive.
If a job spans media and, during the first tape, one of the clean flags is set, the following occurs: the cleaning light comes on and the drive is cleaned before the second piece of media is mounted in the drive.
The implication is that the present job concludes its ongoing write despite a TapeAlert Clean Now or Clean Periodic message. That is, the TapeAlert does not require the loss of what has been written to tape so far. This implication is true regardless of the number of NetBackup jobs that are involved in writing out the rest of the media.
If a large number of media become FROZEN as a result of having implemented TapeAlert, other media or tape drive issues are likely to exist.