Sloppy thinking is rife, particularly in my neck of he woods where it is easy to assume that just because one supplier has a virtual tape library (VTL) it is the same as another supplier's VTL. Well, as the old sales training cliche has it, never assume because to assume is to make an 'ass' out of 'u' and 'me'.

Helmut Muhleis, a principle consultant in FSC's CentricStor VTL area, reminded me of this when I asked him how NetApp's VTL compared to CentricStor, FSC's VTL. "NetApp's NearStore is not a virtual tape library, definitely not," he said.

Why not? "Because it emulates a tape library; it doesn't virtualise it."

But it stores backup files on disk and spoofs the backup application that it is a tape library. Isn't that what a virtual tape library does? Any VTL? What does he mean?

What he means is that it, and most other so-called VTLs (his sense as I see it) emulate tape libraries; they don't virtualise them.

I asked for an example and he obliged.

Suppose you backup a set of server files to a piece of software spoofing the backup app that it is a tape library, and you identify the disk file target as a 200GB LTO2 tape in the 'virtual' tape library and give it a barcode of 'TPE14062006'. This is fine and the backup is done. When you then want to write it to tape, to an actual physical tape drive, you have to write to, specifically, a 200G LTO2 tape with a barcode identifier of 'TPE14062006', exactly the same. No deviations allowed. Also the server backup app has to EXPORT it, has to tell the 'virtual tape library' to write it to tape.

Muhleis says a true virtualising tape library wouldn't restrict you like this. A fully virtualising tape library, like CentricStor, will write the backup in its apparent 200GB LTO2 tape, barcode 'TPE14062006' to a StorageTek 9840 tape with a barcode of 'ANYTHING-YOU-LIKE', or to a DLT or SDLT tape. It can do such conversions itself becase it has its own processor and a full set of software. It can do this without reference to the backup application and it can deal with a variety of tape libraries too.

Muhleis gave another couple of examples. To make a copy of the written tape a partially-virtualising VTL has to do a copy. CentricStor can do two writes simultaneously as it can be split into two separate VTLs for disaster recovery purposes.

CentricStor can manage a real tape library and refresh tapes automatically. If it finds a tape is unreadable it re-create a fresh copy from the separated-off VTL and put it in the prime VTL. Other suppliers' VTL, or, in his term, ETLs (for emulating tape libraries) cant do these things.

These emulating VTLs include the Falconstor-based ones from EMC (Clariion Disk Library) and Sun (VTS Plus, the open systems VTL), and NetApp's Nearstore VTL.

As another way of expressing the difference between CentricStor and the other VTLs Muhleis says CentricStor is a full appliance whereas the others are not.

Other CentricStor attributes

Muhleis said that CentricStor has a co-processor to do compression. So, unlike the FalconStor-based VTLs and their ilk, switching on compression doesn't drastically degrade throughput. Netapp's NearStore VTL also has hardware-based compression.

CentricStor in Europe and the US should have Unisys mainframe support added by the second quarter of next year.

It will have single-instance file storage, which he called de-duplication (although Avamar and Diligent and Data Domain might well disagree), in version 4 of the CentricStor software next year, due for the end of Q2 or Q3 next year. He thinks a 10:1 reduction ratio could/should be achievable.

There are two new CentricStor models. The VTA 1500 is a smaller and less expensive version of the existing VTA 2000. The VTA 500 is a feature-reduced version of the VTA 1500 which is even more affordable.

So far more than 550 CentricStor appliances have been sold: 100+ in Japan by Fujitsu; and 450 by FSC in Europe and the USA. FSC still aim to lead the world-wide VTL market, defined in part by it as a disk-to-disk-to-tape (D2D2T) market.

If the dedupe ratios from Avamar, Diligent and Data Domain really do achieve the 25:1 or thereabouts that's promised than FSC will have a fight on its hands. It's probably got the most completely virtualising VTL on the market, and one that supports more hosts, both mainframe and open systems, than any other VTL product.

But it better keep an eye on the Diligents of this world. Sloppy thinking and over-easy assumptions are unwanted wherever they occur.