Quantum DLT tape drive challenges LTO

A new tape model from Quantum comes out about every two years, and it arrived as expected early this year in the form of the DLT-S4.

The first and most apparent novelty is its name: Quantum dropped the “super” from the unit’s name and has returned to the original initials for “digital linear tape,” discontinuing the adjective that characterized the first two models, the SDLT-320 and the SDLT-600.

Being outsold these days by faster LTO (Linear Tape-Open) devices, the DLT proprietary technology is no longer the most popular choice for this class of tapes. Quantum hopes to reverse that trend by offering exceptional capacity, as much as 1.6TB of compressed data on a single reel. Moreover, Quantum is making DLTSage, its formidable management application, an integral part of the device drivers for the new tape.

The DLT-S4 offers twice the capacity-per-reel of its LTO-3 rivals, and Quantum makes this technical advantage even more appealing with an aggressive price. The DLT-S4 is only slightly more expensive than the SDLT-600 or LTO-3 devices that offer half or less the recording capacity. The DLT-S4 also puts away data at more than twice the speed of its predecessor, with a nominal transfer rate as fast as 120MBps with compression.

A third arrow in Quantum’s quiver is one of DLTSage’s additional features that will password-protect each reel created with the DLT-S4. The password protection is probably a placeholder for more advanced, future security options such as built-in encryption, but it certainly has the potential to grab customers’ attention.

Hefty test bed required

Tapes with performance and capacity levels of the DLT-S4 call for test-bed components capable of doing some heavy lifting. I tested the new tape on a Windows server 2003 machine where I had set up eight Western Digital Raptor 74GB drives and an LSI Logic MegaRaid controller in RAID 5 configuration.

Iometer testing on that LUN measured transfer rates faster than 180MBps, more than enough to challenge the DLT-S4. I connected the desktop tape’s Ultra320 SCSI interface to an Adaptec 39320 controller on the same server.

The DLT-S4 has the same lunch-box shape as its predecessor, the SDLT-320, but a closer look at the back of the unit reveals some layout changes, including a different location of the SCSI controls, fan, and power supply.

The front of the unit is mostly the same, but I appreciated a larger eject button, which sits flush with the cover to make involuntary maneuvers less likely.

Quantum bundles the tape with a full license of Symantec Backup Exec 10, which I used for most of my test scripts; however, I also had no problems running backups and restores with other applications such the native Windows Backup and CA BrightStor Arcserve.

No security slouch

If you store sensitive data on your tapes, DLTSage’s security features alone are reason enough to deploy a DLT-S4. To test that feature, I launched the application and clicked on the Tape Security tab. A new window opened, giving me the option to add a security key and to instruct the tape driver to add that key to all cartridges created on that unit.

DLTSage is not too fussy about the keys you assign and will accept anything between eight and 32 characters. It’s important to note that there are no backdoors to uncover a forgotten key, which makes data disclosures difficult but also makes Tape Security vulnerable to forgotten-password reprisals. Without the right key, you won’t be able to access the cartridge from any application.

After setting tape security, my backups and restores ran without problems, as long as I provided the correct key.

Slow but steady

To fill up the exceptional capacity of the DLT-S4 reel, I ran a sequence of scheduled full backups of my server, which is similar to how the tape drive will be used in the real world. 

At 65GB for each run, it took many backup cycles before my backup application, Veritas BE (Backup Exec), asked to mount another cartridge. Checking the BE statistics, I saw that the tape had stored a whopping 785GB of uncompressed data, very close to its theoretical limit.

Tape performance was also close to the drive limits, as fast as 108MBps with compression, but to reach similar results you would need something of a “perfect storm” of components, including data that could compress well and a source disk system (like my Raptor array) that could sustain that transfer rate.

The Quantum DLT-S4’s remarkable speed is still well behind the nominal 160MBps of the LTO-3, but customers might appreciate its large capacity, moderate cost, and powerful management features. Clearly, the tape format war in the mid-tier market is not over yet.