Product Reviews

Exabyte is in the habit of making its VXA customers nervous, with each new format generation taking an inordinate amount of time to materialise. In fact, when we looked at Exabyte's VXA-2 format, we hoped Exabyte wouldn't keep us waiting three years for VXA-3, but it's done just that.

The latest VXA-320 represents the third generation of this format and follows on from VXA-2, which was launched in 2002. The wait was worthwhile, as the VXA-320 delivers a doubling in native transfer rates to 12MB/sec and a native capacity increase to a useful 160GB 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 recognised but automatically ejected.

What makes the VXA format stand out are three unique technologies aimed at providing reliable data restoration. Discrete packet format (DPF) breaks down data into packets before writing them to the tape. During a read operation, the packets can be read back in any sequence, as they're reassembled in the drive's buffer before being sent to the host. Packets that are correctly retrieved on the first pass of the head

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are stored in the buffer. Subsequent passes are then carried out until all the packets are read in, and the data string is assembled before being forwarded to the host. Variable speed operation (VSO) allows the drive to adjust tape speed to match the data flow, and avoids the problem of the drive stopping and repositioning the tape whenever the data flow is interrupted. During write operations, an overscan operation (OSO) is used to scan the data and rewrite it if an error is detected.

For performance testing, the drive was installed on a dedicated Ultra320 SCSI controller in a dual-Xeon system running Windows Server 2003. At the time of review, EMC was the only backup software vendor to have a patch on its website for native support, so we called in its Dantz Retrospect 7. We used a 15GB mixture of data typically found on a workgroup or SMB server and asked Retrospect to back up, verify and restore the test data. Backup operations were impressive, as the drive secured the test data at a rate of 13.1MB/sec - marginally above the quoted native transfer rate. Speed dropped slightly for data verification, with Retrospect reporting 10.1MB/sec. But this picked up again for the full restoration task, with this returning 12.4MB/sec. We also ran a basic backup test on unpatched versions of Symantec's Backup Exec 10d and CA's ARCserve for Windows 11.5 and saw them return 11.9MB/sec and 12MB/sec respectively.

With HP resurrecting DDS via the DAT72 format, competition is getting even tougher for the SMB backup market space. As discussed in the Freecom USB DAT 72 review, we now know that HP expects to release a sixth generation of DDS, or DAT160, early in 2006. So fears about its longevity seem to have been allayed. Nevertheless, VXA does offer some strong competition to DDS, with the VXA-320 delivering on the quoted performance figures.