Ecrix apparently started with a clean slate when it developed the VXA format.
The cartridges bear a striking resemblance to AIT cartridges for example, but externally the notable difference is the lack of data contacts on the back of the VXA cartridge.
While all the other formats described here can be called streaming tape formats, VXA is not. In fact, it's a Discrete Packet Format (DPF).
In simple terms the other formats take all the data from your server and lay it on the tape as a constant contiguous "chunk" while VXA breaks the data stream up into packets with each packet containing 64 bytes of data in addition to sync, addressing, ECC and CRC data.
The VXA format has a capacity of 33GB native and 66GB employing a 2:1 compression ratio while data transfer speeds are up to 3MB/s native and 6MB/s compressed.
Compression
Even though most vendors claim a 2:1 compression, up to 30:1 compression rations have been achieved with extremely compressible data.
It is not uncommon at some sites to find compression ratios ranging between 3:1 and 5:1 depending on the data.
Cartridge Life
Generally vendors rate the tape life as less than five percent loss in magnetisation at 20 degrees Celsius and 40 percent non-condensing humidity. It is interesting to note the difference between "passes" and "uses". For helical scan tapes they both effectively mean the same thing.
However, for linear technology tapes, the head may make up to 56 "passes" of the tape in one "use". To put this in perspective, Quantum claims a life of 1 million passes for its SDLT220 tapes, but this only equates to 17,850 uses.
Steven Turvey is lab manager at RMIT Test Labs. RMIT IT Test Labs are an independent testing institution based in Melbourne, Victoria, performing IT product testing for clients such as IBM, Coles-Myer, and a wide variety of government bodies.
