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
- ↑ Phone call with Tandberg technical support, speaking to a former Exabyte engineer on July 2, 2010.
- ↑ Exabyte whitepaper describing VXA Packet Technology
- ↑ Another VXA Packets explanation
- ↑ Exabyte's DDS to VXA migration sales pitch
- ↑ Exabyte's DLT to VXA migration sales pitch
- ↑ ECMA-316. 2001. pp. 54, 77–83.
External links
 |
Wikimedia Commons has media related to VXA. |
- ECMA 316 Specification of VXA-1.
- ECMA 222 Specification of ALDC, the data compression standard for VXA-1.
- VXA Alliance