VXA

VXA is a tape backup format originally created by Ecrix and now owned by Tandberg Data. After the merger between Ecrix and Exabyte, VXA was produced by Exabyte Corporation. On November 20, 2006, Exabyte was purchased by Tandberg Data that has since stopped further development of the format.[1]

How it works

Exabyte and Ecrix describe the data format as "packet technology."[2] Since VXA is based on helical scan technology, data is written across the tape from side to side in helical strips.

The novel part of VXA packet technology is that each stripe starts with a unique packet ID and ends with an ECC packet checksum. As each stripe is written to tape, it is immediately read back to verify that the write was successful.

If the write was not 100% successful the packet can be rewritten at another point on the tape without stopping. When the data is read back, the packets are reassembled into a "buffer" by their packet ID.[3] The buffer has 3 additional ECCs to ensure data integrity.

Another aspect of VXA is that there are 2 read heads for each stripe, slightly offset in relation to each other to allow for more flexibility in reading tapes written by other drives.

Due to the relatively slow tape speed inherent to helical scan technology, the drive is able to stop and start the tape much more quickly to avoid the need to backhitch.

Market context

The VXA format competes mainly against the DDS,[4] and DLT-IV[5] formats.

Overview
Generation VXA-1 VXA-2 VXA-3 VXA-4 VXA-5
Release Date 199920022005UnreleasedUnreleased
Max Native (uncompressed) Capacity (GB) 3380160320640
Max Speed (MB/s) 36122448
Encoding EFM[6]PRML
Track width 9.1 μm5.7 μm
Head FerriteTFMR

VXA-3

Exabyte released two different product lines based on VXA-3 technology, VXA-320 in 2005 and VXA-172 in 2006. VXA-172 drives are limited to 86 GB per tape cartridge, but can be unlocked (for a fee) to remove the limit. They are otherwise the same. VXA-3 was the first helical scan system in production to feature thin film MR heads.

Notes
  • Data Capacity figures above are for uncompressed data. Exabyte assumes a 2x compression factor in their marketing material.

Media

Media was released on two families (V and X), with different capacities based on the length of the tape, and the drive it is being used in.

Product V6 V10 V17 V23 X6 X10 X23
Length (Meters) 62m107m170m230m62m124m230m
Native Capacity (when used in the given type of drive - empty means not compatible)
VXA-112 GB20 GB33 GB
VXA-220 GB40 GB60 GB80 GB20 GB40 GB80 GB
VXA-17240 GB86 GB
VXA-320160 GB40 GB86 GB160 GB

Cartridge / tape
  • VXA tape V17 (170m), top view
  • VXA tape V17 (170m), bottom view
  • VXA tape V17 (170m), partially disassembled
  • VXA tape V17 (170m x 8mm) magnetic tape, no cover

Mechanism / drive
  • VXA-1 tape drive, front bezel view
  • VXA-1 tape, drive, cover removed, top front view
  • VXA-1 tape drive, cover removed, top view
  • VXA-1 tape drive, rear view, showing ATAPI interface
  • bottom rear, showing original and rebrand labels
  • front view, cover and bezel removed, rotary head visible

Tape and drive together
  • VXA-1 tape drive with tape inserted
  • VXA-1 tape drive with tape loaded and threaded
  • VXA-1 tape drive with tape loaded, view from right side
  • VXA-1 tape drive with tape loaded, view from rear left

References
  1. Phone call with Tandberg technical support, speaking to a former Exabyte engineer on July 2, 2010.
  2. Exabyte whitepaper describing VXA Packet Technology Archived 2010-08-22 at the Wayback Machine
  3. Another VXA Packets explanation
  4. Exabyte's DDS to VXA migration sales pitch
  5. Exabyte's DLT to VXA migration sales pitch
  6. ECMA-316. 2001. pp. 54, 77–83.
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