IBM Mainframe Forum

I was asking our storage administrators about an IEF343I error received while trying to copy data from a very old GDG.

They answered: there is no entry for this GDG in the RMM catalog, since it's very old.

I am trying to understand what this answer means exactly. The GDG is still viewable and was stored as tape. If it is not referenced in storage catalog anymore, would it mean that its listing in Data set List utility is an empty pointer?

Thank you for your help,

You have to decode what RMM means: Removable Media Manager. "Removable media" is a term that collectively describes "media" - tapes, disks or what have you, that is not permanently available to the system. When RMM was originally devised it also meant optical media - CD disks, for example, but they have largely gone away. These days "removable media" means tapes.

RMM is a system that maintains a data base of the tape volumes it knows about. A characteristic of removable media is the data typically carries an expiration date. When the data is created it is assigned an expiration date. In JCL this is assigned by the EXPDT (expiration date) or RETPD (retention period) parameters. It is also sad, but true, that the magnetic data on tape volumes literally wears out. Back in the 1960s when I started in the business, data on magnetic tape often disappeared after a very short - 2 or 3 years - time. In other words, you could not depend on leaving the tape to just sit around and get the data back. It's longer now, but it's still not indefinite. There were steps you could take to extend this life - just spinning through the tape from time to time often extended the useful life of the data on the tape - or simply copying the data to a new tape also worked, but ultimately it required active management of the data. This management was rarely performed.

In any event, many times magnetic tapes are simply discarded after a few years simply because it is not safe to record new data on the tape. It is also sad, but true, that the drives used for the tape are discarded. A 7 track tape that I created in 1966, for example, simply cannot be read even if the data is still on the tape because there are no longer tape drives capable of reading the tape.

It sounds like the dataset is still in the system catalog, but has been dropped from RMM. Try locate the dataset in RMM using the RMMSD command hint: TSO HELP RMMSD). You might need to specify OWNER(*) as I recall.

Steve, you are then suggesting it could be a hardware failure. Very interesting. Do you know (I am slightly digressing) what form take the tapes nowadays?

Willy, thank you. I have looked through the RMMSD command and admit it is very furnished. I shall try to make it work.

No. I am suggesting the tape library discarded the tape because it was too old. A hardware error would be indicated by a failure to read the data on the tape.

Back when I started magnetic tape was on large round reels. In the 1980s magnetic tapes switched over to cartridges. Depending on where you were the new tapes often were called "square" tapes to distinguish them from the old, round tapes. Obviously, new drives. Square tapes were much more reliable than round tapes, and much easier and more reliable to load than round tapes.

Within 10 years or so the first tape library robots appeared. Just a few drives (compared to the way machines were configured before) were hooked to the robots. The robots retrieved the cartridge, handed them off to a drive, and retrieved the used tape from whatever drive took the tape and stored it in the robot library when the drive was finished with the tape. In another 10 years or so "virtual" tape started up. "Virtual" tape got its start because much tape capacity was wasted; just a few megabytes on tape with gigabyte capacities. "Virtual" tape used robots and, obviously, software to stack multiple logical tape volumes on real tape volumes. Many times you're using virtual tape and it takes some detective work to deduce it's all smoke and mirrors.

On this site are videos. There is one video of an alleged 1970s machine room, but after analysis it was from the 1980s. It showed both round tapes and tape drives and some early cartridge tape drives. Look it up and watch it.

and then there was the IBM 3850 mass storage system

Oh, yes, the 3850 and its plastic beer cans. The IBM tape library is largely based on the robotics for the 3850.