The VXA format was originally developed by Ecrix Corporation back in 1999 and acquired a couple of years later by Exabyte when it realised it needed a new product line to prop up its Mammoth tape drive line. VXA offers some interesting and unusual features and has always been aimed primarily at existing DDS users looking for a reliable migration path.
One of the main aims of VXA is to provide reliable data restoration and it uses three unique technologies to achieve this: discrete packet format (DPF), variable speed operation (VSO) and overscan operation (OSO). DPF is used to break data down into packets before writing them to the tape. Each packet consists of 64 bytes of user data, synchronization markers and address information plus error correction codes. During a read operation the packets can be read back in any sequence as they are reassembled in the drive's buffer before being sent to the host. Packets that are correctly retrieved on the first pass of the head are stored in the buffer. Subsequent passes are then carried out until all the packets are read in and then the data string is assembled before forwarding to the host.
VSO allows the drive to adjust tape speed to match the data flow. This avoids a problem common to tape streamers called 'shoe-shining' which occurs when the data flow is interrupted and the drive has to continually stop and re-position the tape. Maintaining a constant speed can reduce tape and drive component wear significantly. During write operations, OSO is used to scan the data and rewrite it if an error is detected. On read operations, all heads on the rotating drum are used to make multiple scans so correct track geometry and pitch are unimportant. The key benefit here is that Exabyte guarantees that a tape created on one VXA-320 drive can be read on another.
The VXA-320 delivers a fair turn of speed with a native transfer rate of 12MB/sec and partners this with a useful 160GB of storage capacity on compact 8mm cartridges. Full backward compatibility with VXA-2 extends to X23, X10 and X6 media which uses thinner tape than the older VXAtape V6, V10 or V17 media. If an older tape formatted on a VXA-1 drive is loaded in the VXA-320 it will be recognized but will be automatically ejected. And the VXA-320 delivers on the quoted performance figures, returning 12.1MB/sec for backup and 12MB/sec for data verification although speed dropped down to only 8.4MB/sec during restoration tests.
With so many different formats competition is now getting even tougher for the SMB backup market space. Despite this, and the fact that development time for each VXA generation has been comparatively slow, it has delivered each time making it a solid alternative for small businesses looking for an alternative format to DDS and DAT72.
Verdict
The VXA-320 delivers on Exabyte's performance and capacity promises and looks a very worthy alternative format to DDS and DAT72
Format: VXA-3 Native storage capacity: 160GB Native transfer rate: 12MB/sec Interface: SCSI Ultra160 Buffer: 8MB Backward compatibility: write - V23, X23, X10, X6; read - V23, X23, X10, X6 Recording method: 8mm helical scanning Media: 160GB X23 cartridges - £42 exc VAT
