Tape Drive Showdown
Tape technology continues to evolve and has remained relevant despite innovations in the storage market. Even with advances in disk-to-disk backup and optical storage, for example, IT managers continue to rely on tape for its proven reliability.
During the past few years, a number of improvements have been made to the midrange space of the tape market. eWEEK Labs tested three midrange drives that reflect those changes (and that have spent the past year fighting tooth and nail for market share): Storage Technology Corp.s T9940B, Quantum Corp.s
SDLT 320 and an LTO-1 drive provided by Dell Computer Corp. in its PowerVault 122T LTO Autoloader. (Quantums DLT family, which became extremely popular in the 1990s, evolved into the SDLT product line.)
One of the most challenging aspects of testing tape drives is that performance is heavily dependent on the type of data being written to tape.
Most organizations have a mix of compressible and uncompressible data, but the ratio differs widely from company to company. This makes it difficult to create a test scenario that is widely applicable.
When vendors publish performance specifications for their drives, they tend to lean toward theoretical maximum performance numbers, which assume that the data is completely compressible.
With backup windows getting smaller and data stores getting larger, we felt it would be valuable to determine the native capabilities, since overestimating a drives performance would lead to backups that took longer than the available backup window.
To test the native speed of the drives, we used a data set that was noncompressible (MP3 and Zip files). As a result, we were able to determine the worst-case performance scenario for each drive to determine base-line performance capabilities.
Backup Windows Differ
Our test server was a Dell PowerEdge 6400 with four Xeon processors running Computer Associates International Inc.s BrightStor ARCserve Backup Version 9. The server was loaded with 2GB of RAM.
The Quantum SDLT 320 and LTO-1 tape drives were hooked into an Adaptec Inc. SCSI Card 39160, while the StorageTek T9940B was hooked in using a QLogic Corp. QLA2310F 2G-bps Fibre Channel host bus adapter.
The disks in the test server were set up in a RAID 0 configuration to allow for maximum throughput to the tape drives.
With uncompressed data, the StorageTek T9940B drive turned in performance of 29.55MB per second, the fastest of the lot. The drive also has the largest native capacity of the drives tested200GB per tape.
The StorageTek T9940Bthe only Fibre Channel drive of the grouphas carved a niche for itself in what you might call the "ultraenterprise" space: Its a good choice for applications (and organizations) that cannot tolerate big backup windows. However, this security comes at a much higher price than that of the other drives tested: $39,500 per drive.
Second in native capacity per tape (160GB) but slower in performance with uncompressed data (14.99MB per second), the Quantum SDLT 320 is a good choice for organizations that have a lot of data but dont mind bigger backup windows. The SDLT costs between $4,000 and $4,500.
The LTO-1 drive, priced at $4,995, posted a relatively quick score (14.64MB per second), comparable to the Quantum drive in tests. However, the LTO-1 drives native capacity100GB per tapewas the smallest of the group.
LTO-2, the second generation of LTO, has already been released, but we did not get an LTO-2-based unit in time for our tests. (eWEEK Labs will be evaluating the next-generation drives in a forthcoming issue.)
By the end of summer or early fall, Quantum is expected to release its follow-up drive, the SDLT 600. With LTO-2 doubling its capacity to 200GB per tape native and speeds to 35MB per second, the SDLT 600 will have to be a big improvement over the SDLT 320 to stay competitive in the tape market.
Senior Analyst Henry Baltazar can be reached at firstname.lastname@example.org.