I want to add that when you start testing the tape drives, one of the first things that you need to do is to measure the exact capacity of an 18 TB LTO-9 tape c

I want to add that when you start testing the tape drives, one of the first things that you need to do is to measure the exact capacity of an 18 TB LTO-9 tape cartridge. For instance, I write the tapes with "dd bs=131072 if="$file_name" of=/dev/nsa0". This means that I am using 128 kB blocks. I have measured that a 6 TB LTO-7 tape cartridge has a capacity of 45905860 such 128 kB blocks. The position of the read/write head, measured in blocks from the beginning of the tape, can be obtained with "mt rdspos". After you choose some block size, e.g. 128 kB, you should forever stick with it in all your write commands and on all your tapes, so that you will always get consistent information about the position of the read/write head. The tape capacity can be measured by writing files, preferably of the same size that you will typically use for archives (in order to write a similar number of file marks), until you get a write error. With the capacity of the tape known exactly, after any writing of a new file you get the current position and you compute the remaining free space on the tape, to know whether you can still append data or you must change the tape. The position in blocks can also be used to verify that the tape drive works OK. For example when after rewinding the tape you go to the end of the written part, to append new files, you must see the same position as after your last write. Or when writing a copy of a tape, you must see the same positions on both tapes for any file. For retrieving files, the position in blocks does not matter, but only the ordinal number of a file. You position the read/write head to the beginning of a file with "mt rewind; mt fsf $file_number". Then you read the file, possibly in a loop if you want to read multiple consecutive files. For going to the end of the written part of a tape, to append new files, you must use "mt locate -e; mt bsf 2; mt fsf", as I have mentioned in a previous posting. The explanation of why this is needed is buried in the documentation about how tape marks and head positioning really work. Whenever I start using the tape drive, I use "mt comp off; mt status" and I check the status output to be as expected. The tape is ejected with "mt -f /dev/esa0 rewind".