A Closer Look at the Results
In our tables, backup time represents the period during which data was actually being written to tape. During the verify time, the recorded data was checked against the original source. The job completion time is the total of backup time, verify time, and all other overhead; this includes calibrating, positioning, and rewinding the tape, as well as the time the backup software required to process the request.
Comparison of the results revealed both significant and insignificant differences. LTO Ultrium 1 and SDLT devices all scored relatively close across the board on the backup test. SDLT devices had a slight edge in backup and verify operations.
Matters became more interesting when we examined the performance of the Sony AIT-3 devices. Both the single-drive Sony SDX-D700C and the automated Sony StorStation AIT Library LIB-81 were far behind all the other products in backup and verify speeds. This could take on real significance if your data volume is extremely large and your backup window is very small.
But both devices restore speeds were far superior to those of the other products. And since restores are manual operations, this could save administrators a lot of time. When you have ten file-restore requests to process, the difference between 1.5 minutes and 6 minutes per request is no joke. This speed is due to Sonys Remote Memory In Cassette (R-MIC) technology, which uses a built-in chip to store catalog and file location information. This way, the tape need not be rewound for the device to read the catalog from the tape, as with DLT, LTO, or SDLT formats.
LTO Ultrium 2 is the newest technology in our roundup, and at testing time HP was the only manufacturer shipping it. This format greatly reduces backup time—and especially verify time—compared with LTO Ultrium 1. Yet when compared with Quantums SDLT technology, LTO Ultrium 2s overall performance advantage was not eye-catching. Restores were still considerably slower. Throughput can vary significantly depending on the mix of data, and most advanced backup applications offer plug-ins to back up databases or mail servers. Since such backups usually involve data from a consistent source, much higher speeds can be achieved. HP claims a native transfer rate of 30 MBps, a throughput we were not able to duplicate with our setup and data set.
The inventory test revealed relatively minor differences among the devices—with the HP StorageWorks 1/8 Autoloader in first place. But when we retested the Overland PowerLoader SDLT 320 with a second drive installed, it raced through the test in 3 minutes 50 seconds.