VXA Technology by Ecrix and Exabyte

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VXA Technology
VXA tape technology was created by Ecrix Corporation, which entered into a merger agreement with
Exabyte in August 2001. As of November 2001, Ecrix's operations were fully integrated with Exabyte and
now operate under the Exabyte name.
Exabyte will continue to focus its VXA technology on the low-cost market segment. The next-generation
VXA-2 became available in June 2002. The VXA-2 drive offers a compressed capacity of 160GB and a
compressed data transfer rate of 12 MB/sec. VXA-2 pricing is expected to be comparable to the VXA-1 at
introduction. The VXA roadmap includes at least two more product generations following VXA-2. The
VXA-3 is projected to support 320GB of compressed capacity at a 16 MB/sec compressed data transfer
rate, while VXA-4 is expected to offer 640GB of compressed capacity at speeds up to 32 MB/sec
compressed.
VXA offers a unique approach to data recording that allows it to address some of the inherent
weaknesses associated with streaming tape technologies. In order for a linear or helical tape drive to
operate at peak efficiency, large blocks of data must be read or written from the drive while the tape is

moving at a constant speed (or "streaming") to keep the drive's data buffer full. When "streaming" is
interrupted, the drive must reverse direction and reposition the tape before read/write operations can
resume.
VXA uses a proprietary data format and algorithms for data verification and correction. Instead of
formatting data on a tape in long strings, which requires the drive to stream for optimum read/write
performance, VXA breaks the long data strings into smaller packets before being recorded on the media.
VXA's Discrete Packet Format (DPF) uses 64 bytes of user data per packet and 387 packets per track.
Data packets also contain a synchronization marker, unique address information, Cyclic Redundancy
Check (CRC) code and Error Correction Code (ECC).
During a read operation, the VXA drive uses all four leading and trailing heads to scan the tape and read
the data packets into a buffer segment. The packets that compose a data string may arrive at different
times in the data buffer. Because each packet has a unique address, the VXA buffer architecture
efficiently reassembles the packets in the correct order, regardless of the order in which they were
received. The VXA data buffer retrieves data with each pass of the read heads until all data packets are
loaded into the buffer.
Much like other streaming tape technologies, VXA does not rely on precise alignment of heads and data
tracks to read or write data reliably. Instead, VXA reads and writes data in packet form and overscans the
recorded area of the tape. Overscanning requires a system architecture that eliminates the dependency
on the alignment geometry between the tape path and the recording head. To read or write data,
streaming tape devices depend on a constant head-to-tape speed for linear recording or a constant track
angle for helical-scan recording. VXA's technique allows each channel of the drive to scan an area
greater than 100 percent of the recorded area of the tape, ensuring a full data recovery and increasing the
reliability of data interchangeability between different VXA drives.
VXA's Variable Speed Operation enables it to continually adjust the tape speed to match the actual data
transfer rate between the drive and the host. Because VXA can vary the speed at which it sends or
receives data, it is unlikely that VXA ever has to stop the motion of the tape completely. In the rare
instance that data transfer operations do stop, the VXA drive can gently slow down to a "Ready Mode"
and then restart from that location when read/write operations resume. By eliminating tape repositioning,
VXA reduces performance degradation as well as wear on the media and drive mechanism, which can
compromise the reliability of the data.
The combination of VXA's Discrete Packet Format, its ability to alter the speed of the tape to match
available host bandwidth and an overscanning technique which allows data to be read from any physical
location on the tape without having to follow a chain of tracks from beginning to end results in a new and
economical backup technology which is fast, reliable and less sensitive to media errors.