When a new LTO9 tape is first loaded into a drive, the drive will start an initialization process. This process can typically take between 35 and 60 minutes, but can take as long as 2 hours. The default tape mount retries and time between retries applied by DPX wait as long as 10 minutes for a tape to become ready, which is not enough for an initialization to complete. This will cause Write Label and labeling on the fly to fail in most cases.
First, check the vendor documentation for libraries to see if they have tools that will perform the initialization of the media that needs it, so that DPX won't have to wait for it. For standalone drives, simply loading new tapes, waiting for it to complete, unload the tape and repeat should be sufficient, though somebody will need to watch it.
For DPX to tolerate the time needed to initialize the tape, the tape mount retries and retry timeouts need to be increased so that total time is at least 2 hours. Shorter retry timeouts with more retries allow DPX to notice the tape is ready more quickly once the process is complete.
If labeling with Write Label in Operate Library or Control devices, these options need to be applied to the tape mount manager on the device server(s); -t for the retry time in seconds and -r for the number of tries. For -example, -t 900 (15 minutes) and -r 8, would tolerate the initialization taking 2 hours, but wouldn't have to wait more than 15 minutes when it is complete.
If media is added to the database with Add Media, the job that first uses it will label the tape as needed; labeling on the fly. The tape mount manager options also apply to this case, but there are also destination options to set the values for jobs; Tape Mount Attempts (retries) and Mount Interval.
The Frequently Asked Questions page on the LTO.org web site has additional information on initialization; https://www.lto.org/faqs-about-lto/. The vendors of LTO9 drives and libraries supporting them may also have their own documentation.