Like I have said, it is not necessary to dedicate a full-time FreeBSD server for this, you can use either a Linux server that is rebooted temporarily in FreeBSD or a FreeBSD virtual machine on the Linux server.

Around $5000 to $6000 should be enough for a LTO-9 tabletop tape drive plus a suitable SAS HBA card and SAS cable. The card must have matching SAS connectors and SAS speed with the tape drive.

More money will not bring anything extra until a much higher amount is reached, which would be enough to buy a tape autoloader/library, which would eliminate the necessity for a human to insert and remove the cartridges into the tape drive when needed. I am not sure if $50K is enough for a tape autoloader.

Tape autoloaders/libraries are worthwhile only for very big organizations where the amount of data that is continuously written or read to or from the tapes is very large. For a small business or for an individual a tape autoloader is certainly not worthwhile, because the tape drive will be in use at most a small fraction of every day.

1 PB/year is less than 3 TB/day. This can be written on a single tape in a little more than 2 hours. Even with a simple non-pipelined implementation of the file uploading with the writing on the tape, the backup can be done in less than 4 hours. Even writing 2 copies can be done in less than 8 hours. The backup can be done mostly or completely overnight.

For a much bigger amount of data one could buy several tape drives, before starting to think about an autoloader. Also it is possible to pipeline the network transfers with the tape writing, for a backup speed higher by around 50%.

If money would not be a problem and if the data needs to be archived for a long term, so that multiple copies are desirable, I would buy 2 tape drives, to be able to write 2 copies simultaneously.

This would also halve the time for archiving the initial 2 PB of existing data, which will take several months, so a speed-up would be desirable. Having 2 drives will also increase the reliability, as the system will continue to work if one becomes defective.

With only 3 TB written per day, a LTO-9 tape, which has a capacity of 18 TB, will be enough for 6 days.

So unless a backup must be restored, the operator would need to change the tape only once per week.

This is a moderate amount of data, easy to handle with a single drive, even if two are preferable for redundancy and for higher speed.

I do not understand your reference to a "a tape drive holding at least 8 tapes in data center". If you mean an autoloader, from what you describe it does not seem that the very big expense for an autoloader would be justified.

The LTO tapes are best stored in suitcases that can contain 20 cartridges, i.e. when using LTO-9 that is 360 TB. Therefore 3 suitcases store more than 1 PB, i.e. a year of data according to your example. The suitcases should be stored in a secure safe or cabinet. They are usually made to be stackable.

I have assumed that your 1 PB is of already compressed data. If the data is compressible than the requirements for the usage time of the drives and for the storage volume would be much smaller.

I have forgotten to mention that after I compress and encrypt the archived files, I add redundancy with a Reed-Solomon code, e.g. with the par2 program. If I choose e.g. a redundancy of 5%, then a file retrieved from the magnetic tape could have defects of up to 5% of its size, while the original data could still be extracted from it.