The number two mistake would failure to properly configure tape devices to the operating system and backup software. SCSI libraries make use of element numbers to identify drives, slots and robotics. SCSI commands issued by the backup software use those element numbers to target a specific element. On the other hand, the operating system uses SCSI IDs to identify the drives. A common mistake is to define the wrong OS device/element number combination to the backup software thus causing some puzzling errors.
Finally, care should always be taken in configuring the format that will be used to write to the tape drives. Many operating systems will allow system administrators to configure parameters such as block size, rewind, compression, etc. Failure to properly configure those parameters can potentially lead to data access or integrity issues. The vendor's documentation should always be consulted when attempting to configure a tape subsystem.
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This was first published in August 2004