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 who 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	1999	2002	2005	TBA	TBA
Max Native (uncompressed) Capacity (GB)	33	80	160	320	640
Max Speed (MB/s)	3	6	12	24	48
Encoding	EFM[6]	PRML
Track width	9.1 μm		5.7 μm
Head		Ferrite	TFMR

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.

Gallery

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
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.

External links

• ECMA 316 Specification of VXA-1.
• ECMA 222 Specification of ALDC, the data compression standard for VXA-1.
• VXA Alliance