"Near-Line" Archival Storage...

[dabinka]

Greetings to all.

I've got a question. Let me first explain what I want to do.

I need to setup a "directory tree", like /mnt/library or something. Data sits in here available for read/write (since it's sitting on a disk) until a script comes along, and dumps the data to a DLT library (using MTX as the robot control), creating a simple database so it knows where the files are on what tape.

This happens nightly, or every 6 hours.

So, now the directory data has been moved to tape- which is where my question comes from.

How do I create a "placeholder" file- that when I attempt to read/write to it, instead launches a script which retrieves the data, and somehow makes the said data (ether by copying it to the original location and replacing the "placeholder" file) transparently available to the user again- until the file idles for 6 or 12 hours and is moved back to DLT storage?

Moving the data to tape is easy. I'm fine with that. If I even had to, I could just write a script that I feed ether a file path to, a list of files, or a folder to and it restores the data that way. But I'd like to see if the "placeholder" idea is possible- so I can browse the entire directory structure, and then if I cat something or run nano on a file, or copy some MP3 to my desktop, the system launches the background script, and waits until the data is restored to access it. Partially so I can share the said archival directory across my network, and partially because this is what several $$,$$$ programs do.

Any ideas or opinions?

Cheers!
-DB