DLT 8000

Get high-end server backup performance

Quantum's DLT 8000 is the latest in the company's series of fast and reliable tape drives based on the DLTtape technology. The DLT 8000 combines high capacity, speed, and compatibility with earlier DLTtape products to serve the high-end server backup market. The new drive is available with a Low Voltage Differential (LVD) SCSI interface that allows longer cable lengths to connect the drive.

The DLT 8000 offers a 20 percent improvement in speed and a 15 percent improvement in capacity over the DLT 7000. Native (uncompressed) capacity is 40GB and the streaming transfer rate is 6MBps. Quantum added variable speed recording technology to the DLT 8000 to help keep the tape streaming evenly when the computer system can't feed data to the tape drive fast enough. When you enable the tape drive's AUTOSPEED mode, the tape drive monitors the number of repositions and slows the transfer rate from 6MBps to 5.5MBps, or to 5MBps when necessary to keep the drive streaming.

In addition to speed and capacity, the DLT 8000 boasts some impressive specifications. The mean time between failures (MTBF) rating is 250,000 hours at a 100 percent duty cycle, and head life is 50,000 hours. The media rating is 1,000,000 passes or 15,000 uses.

DLTtape technology has several characteristics that contribute to its capacity, performance, and reliability. DLTtape uses half-inch recording media, which provides more recording area than 8mm, DAT, and DDS formats and allows more data storage per tape length. The DLTtape cartridge doesn't contain a tape take-up reel, so the cartridge can hold more tape. DLTtape gets its name from the linear way that the heads lay tracks of data on the tape. Each of the 208 tracks spans the length of the tape. At the end of a track, the drive moves the heads to the next track, and recording resumes with the tape moving in the opposite direction. The result is a serpentine data path written back and forth along the length of the tape.

For testing, I connected the tape drive to a Gateway ALR 9200 Pentium II Quad Xeon system. I used a wide-to-wide (i.e., 68-pin to 68-pin) SCSI cable to connect the DLT 8000 through an Adaptec 2944 Ultra Wide SCSI controller. Installation of the tape drive and its driver was the same as any external SCSI device installation. Using VERITAS Backup Exec 7.3 with the options Write Checksums to Media and Hardware Compression enabled, I backed up a 7GB directory containing 48,216 files in 3315 subdirectories that resided on a RAID 5 array consisting of four 10,000rpm Ultra 2 LVD hard disks. Next, I restored an 807.3MB subdirectory with 7932 files to one 10,000rpm SCSI hard disk and to the RAID 5 array. In this test, the backup took 21.1 minutes at a rate of 5.35MBps and the verification took 28.9 minutes at a rate of 3.90MBps. The restore to the single disk took 5.5 minutes at a rate of 2.44MBps. The restore to the RAID 5 array was much slower than the restore to the single disk, taking 8.2 minutes at a rate of 1.63MBps. The notable restore speed difference between the RAID 5 array and the single SCSI hard disk shows the performance cost that the parity calculations inherent in RAID 5 write operations exact.

To test the native speed of the drive, I ran another backup test with Hardware Compression turned off. This time the backup took 22.8 minutes at a rate of 4.96MBps, which is about 82.7 percent of the DLT 8000's speed rating. Although these results fall short of the rated throughput capacity of 6MBps, they're still respectable.

The DLT 8000 provides worthwhile improvements over the DLT 7000 in terms of speed and capacity. This drive promises to be a solid performer when you use it with systems that can feed data near the drive's rated speed. Starting at $6000, this drive will appeal to businesses that are willing to pay for top performance.

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