Luminex has announced a 3490-type control unit that lets mainframe users backup files to LTO and DLT tape libraries. Currently IBM offers mainframe users its Enterprise Tape Libraries which support IBM's proprietary 3590 and 3490E tape formats. They might also choose StorageTek libaries which support StorageTek's 9840 and 9940 formats.

Mainframe users appear locked in to their tape supplier. Typically enterprise Windows and Unix servers backup to LTO or SDLT/DLT tape libraries from suppliers such as ADIC, Overland Storage and SpectraLogic. Mainframe operating systems, such as z/OS, don't support such libaries or the LTO and SDLT/DLT formats. Open systems libraries rarely support mainframe ESCON communication channels and don't support IBM proprietary tape formats.

What Luminex has done is to create an IBM-compatible 3490 control device which takes in IBM Enterprise Tape Library commands and data from the mainframe but outputs LTO or DLT commands and data streams to an open systems library accessed over a Fibre Channel SAN or a SCSI link. This means, Luminex says, mainframe users can now buy cheaper open systems libraries and tapes.

The Luminex Virtual|BLUE 3490 product is a rack-mounted unit with a Sun processor running Solaris 2.8 and the Luminex Virtual|BLUE 3490 software driver. It connects to the mainframe via ESCON using 1 - 8 physical channels. The mainframe can run MVS, OS/390, x/OS or VM/VSE.

Luminex claimed mainframe users hadn't been able to consolidate and centralise their mainframe and open systems libraries into one storage resource. Also, the acquisition cost and per-reel tape costs of LTO/DLT libraries are significantly lower than those of IBM's Enterprise Tape Libraries.

IBM spokesperson Danny McKissock, EMEA tape marketing manager, asked why IBM enterprise-class tapes are better for mainframes than LTO or DLT tapes, said, "It's dead simple. Mainframes use tapes on-line. It's not a device used for one big backup or archiving. We designed our enterprise tape drives for start:stop operation. We designed LTO, with HP and (Seagate/Certance) to be a (backup/archive) streaming drive for open systems with interchangeable cartridges between suppliers."

IBM, along with H-P and the Certance part of Seagate (now owned by Quantum) developed the LTO format and sells it to Windows, Linux and Unix server users, but not to its mainframe customers. IBM also sells a range of Ultrium tape libraries to its i-, p- and x-Series server customers but not to its z-Series (mainframe) customers.

Why doesn't IBM supply its LTO systems to its mainframe customers? McKissock said: "If you put streaming (LTO) tape in the mainframe start:stop environment it can't handle the back-hitch. The data is written in different places. It isn't sequential." The drive wouldn't be able to stream the data and its performance would be slow.

Back-hitch? If data arrives at a drive slower than its stream speed, it stops. When the buffer is filling up again the tape is rewound to before the last write point, stopped, then started and accelerated to streaming speed and data writing re-started just after the last write point. This re-positioning, re-starting operation is called a back-hitch and takes a lot of time. In the mainframe environment it happens a lot and IBM says its drives are designed for this. LTO and DLT drives are not.

Also IBM has moved on from the 3490 controller and ESCON. FICON delivers 100MB/s full duplex while ESCON is only 15-18MB/s one way (simplex). Newer 3590 controllers are faster and more advanced than the older 3490.

On the 3592 IBM drive the reel keeps moving even if the data arrives too slowly. The data gets written with gaps between the segments. When the drive has a moment it reads all the separated data segments into a buffer and then writes it back to the tape as a continuous stream, thus recovering the gaps in what McKissock called a virtual back-hitch. LTO and DLT drives can't do this. McKissock also says that IBM's enterprise drives have better servo motors for tape positioning.

McKissock thinks that if you put an LTO drive into the mainframe environment it would probably be slower-performing than an enterprise-class tape drive and not as efficient in space usage: "The only advantage I can see is cost, but the performance would suffer."

Will IBM now sell its Ultrium tape libraries to mainframe customers by providing ESCON or FICON connectivity? McKissock said there are no plans to do so. It's horses for courses: start:stop online tapes for mainframes; streaming tapes for Windows and Unix.