Latest generations of LTO and SDLT prove speedy and capacious
Although various industry pundits have repeatedly predicted the imminent death of tape drives, tape backups are still irreplaceable in many business-continuity strategies. Backing up to disks may cut down on downtime, but it’s no substitute for low-cost, long-term data storage and archiving.
Indeed, despite the abundance of alternative backup options, tape technologies continue to evolve, leading to devices that are faster, more capacious, and capable of storing data reliably and at moderate cost. Nowhere is that technological effort more apparent than in the midtier enterprise segment, where Quantum SDLT (Super Digital Linear Tape) competes with LTO (Linear Tape-Open), a technology developed by the triumvirate of Certance, Hewlett-Packard, and IBM. (Notably, Quantum recently acquired Certance, putting the company in the unique position of having its say in the development of both technologies.)
Responding to the challenge posed by alternative backup solutions, backers of both LTO and SDLT have released very fast drives and large-capacity reels like never before. Both technologies have clearly drafted road maps that essentially promise to double performance and capacity every two years. Because the milestones for each road map fall on different schedules, picking a point in time for comparison might favor one or the other. In fact, at the time of this writing, Quantum SDLT is still in its second generation, with four more to come; LTO has reached its third generation, called LTO3, with another three to come.
For the roundup, I tested the latest models based on the two opposing technologies, contrasting the single-tape Quantum SDLT 600 with the LTO3-based HP StorageWorks Ultrium 960 and the Certance CL 800.
After using these drives for several months, I’m comfortable recommending all of them. However, their differences and varying requirements may dictate which one is right for your organization.
The two LTO3 devices win hands down in capacity and performance, with the HP tape running slightly faster than the Certance. Even considering only their nominal, uncompressed transfer rate, LTO3 more than doubles the performance of SDLT600, whereas the capacity is just one-third more. Additionally, whereas Quantum’s SDLT tapes must be formatted manually for WORM, LTO tapes can be conveniently purchased in WORM format.
By contrast, the Quantum unit is less expensive, and so are its cartridges. Quantum drives also have a slight edge on management, with a rich set of diagnostic and monitoring tools that outshine Certance’s and HP’s more basic utilities.
HP StorageWorks Ultrium 960
For the review of this LTO3 tape drive, HP offered me a choice between a unit with a transparent shell and one with a conventional casing. Both, I was assured, were the same production units customers would buy, but the transparent shell would allow an unimpeded view of the device’s internal mechanism and easy monitoring of the tape movements.
I couldn’t resist choosing the one with a transparent case, and I’m glad I did: Looking at the tape motion gave me a better understanding of how some of its features work.
Seeing is believing, and nothing beats seeing with my own eyes how, for example, LTO3’s data-rate matching feature automatically speeds up or slows down the tape to adjust to the computer’s data flow. This approach ensures never having to stop a backup to reposition the tape. Indeed, as I looked through the cover, I saw that the tape was constantly winding or rewinding with a fluid motion, which is one of the reasons for its exceptional performance.
Like any other tape, an LTO3 tape cannot crunch data faster than the server delivers it. To provide proper transfer rate for the 960, HP also sent a ProLiant DL380 server with dual Ultra 320 SCSI controllers running Windows Server 2003. Attached to those controllers were four disk arrays, each hosting four LUNs (logical unit numbers) spread across seven drives. That configuration allowed me to run backups and restores over a maximum of 16 concurrent data streams, which created a data flow consistent with the capability of the tape.
To take advantage of those multiple streams, the server had installed on it HP OpenView Storage Data Protector, an application capable of running multiple concurrent backups to the same tape. For consistency, I used the same test bed for the Certance and Quantum devices.
That layout may seem like (and probably is) overkill for desktop tapes, but it’s important to understand that to really benefit from the additional speed these units provide, it may be necessary to pull data faster from your actual servers and storage devices.
The reward for putting together this test bed was immediately apparent. As I backed up 21GB of highly compressed data from a single LUN, I measured a transfer rate of just 68MBps.
Although this is the best speed the Quantum SDLT600 achieves, the HP tape does better. When I ran a concurrent backup of similarly compressible data from four volumes, the transfer rate jumped to almost 90MBps. Putting together streams from eight volumes pushed the transfer rate to 125MBps, whereas my best effort with a concurrent backup from 16 LUNs clocked in at more than 130MBps.
Consolidating data flows from multiple streams gets the best performance out of the LTO3, although your data might not compress as well as did my test files. Nevertheless, even at lower compression rates, the speed gap between the LTO3 and other tapes warrants a serious reassessment of your backup infrastructure. After all, it’s the fastest tape money can buy, and your business may need the reduced backup windows from using the HP Ultrium 960.
Certance CL 800
Last fall, prior to being purchased by Quantum, Certance was the first vendor to put an LTO3 drive on the market, and the company was equally quick to offer a bundle that includes a copy of the NetVault backup application by Bakbone, plus the convenient protection of a three-year warranty.
The desktop model of the CL 800 is a fraction of an inch wider and taller than the Quantum unit, but it’s slightly less deep. The front of the drive has a cartridge opening and a set of four LEDs to monitor power, activity, errors, and overall status of the drive.
Pushing a single button conveniently located on the right of the feeding slot will automatically load or unload the cartridge. By contrast, on the SDLT600 you have to manually push the cartridge inside the unit, although you use a button to eject it. As expected, all the other controls and connectors are located in the back of the unit.
Certance has loaded its LTO3 tape unit with a handful of features that improve the cartridge life and should grant more reliable backups running at the fastest rate the host sustains. Probably most interesting about these new features is that they don’t require any special settings; the tape drive will automatically “do the right thing.”
For example, from a range of 13 speeds, the tape automatically chooses the best match according to how fast or how slow the host is. Also, in case of power failure, the CL 800 uses a small reserve of electricity to automatically stop the medium and maintain the proper tension.
During a backup the tape automatically verifies the data at four different stages. Moreover, the CL 800 has a dedicated and isolated chamber for the tape, which according to Certance extends the cartridge life to 500 backups, twice the competitors’ cartridge life.
Installing the CL 800 isn’t difficult, but Certance bundles a CD so loaded with extensive documentation, drivers, and diagnostic tools that an incorrect setup is virtually impossible.
Perhaps Quantum will extend its diagnostic apps to also support LTO drives, but I didn’t miss that in my test. The TapeRx application bundled with the tape covers all the diagnostic tasks a user may need.
For example, I was able to see and change tape settings such as automatic compression or speed, check the tape log for errors, and run short read-and-write tests. My tape seemed to be working well, so I moved to install the bundled version of NetVault and run some backups.
For consistency, I attached the Certance unit to the same HP server I used for testing the HP tape drive, and I ran the backups using the same HP Data Protector. As with the Ultrium 960, I expected the CL 800 to be faster than the SDLT 600, but the difference in performance was still striking. For example, the CL 800 crunched a 315GB backup from 16 volumes in less than one hour, finishing almost 20 minutes faster than the SDLT 600. However, the Certance still lagged behind the Ultrium 960 by 15 minutes.
In daily operations, saving that time makes a big difference, which — together with other friendly features of the CL 800 — makes the drive a great value.
Quantum SDLT 600
For my review I received from Quantum a single SDLT 600 tape drive, a shoe-box-shaped, 12-inch-deep unit with an almost square section roughly 7 inches wide. The clean front displays the cartridge opening, three control LEDs, and a tape-eject button. The SCSI connectors, address selector, power connector, and power switch are located in the back.
I didn’t like that the cartridge slot lacks a dust-protection cover. Although, to be fair, no problems emerged during the months I had the unit in my lab, and the other two drives in this group have a similarly unprotected slot. Interestingly, the front of the unit hosts an infrared port accessible for diagnostics from properly configured devices.
For this line of tapes Quantum has developed DLTSage, a unique set of management applications that simplify diagnostic and administrative tasks from a variety of platforms including PDAs and other infrared devices.
Part of DLTSage are the iTalk and xTalk apps. The first connects to the drive via an infrared port; the latter communicates via standard host connections. Both programs are downloadable from the Quantum site and make possible the collection of a wealth of diagnostic data that simplifies troubleshooting and predicting hardware or media faults.
Testing the WORM capability of the tape drives in this roundup wasn’t in my plans, and there isn’t much to test anyway, but Quantum has taken a unique approach to the technology that warrants attention. Whereas other vendors implement WORM using another set of cartridges, Quantum offers another DLTSage application, DLTIce, which transforms regular media into the WORM format and protects it with a unique electronic key.
Turning one of my cartridges into a tamperproof medium was easy enough. I downloaded and installed the latest firmware, clicked the DLTIce icon, and in just a few seconds my cartridge was WORM-compliant.
Quantum suggests a native maximum transfer rate for the SDLT 600 of 36MBps, which more than doubles the performance of the previous SDLT 320 but falls short compared to the incredible speed of LTO3 drives.
Predictably the SDLT 600 was the slowest tape in this group. Nevertheless I measured a maximum backup transfer rate of about 70MBps using eight concurrent streams. Interestingly, the performance of the Quantum drive didn’t improve when backing up from 16 volumes; in fact, the transfer rate was just a few notches lower at 67MBps.
The performance difference compared to the other tape drives is remarkable: It took the Quantum drive almost one hour and 20 minutes to complete a backup of 315GB highly compressible files, whereas the two LTO3 drives finished in less than one hour.
Those records are usually short-lived in this business, and the upcoming next-generation SDLT drives will probably recoup that performance gap. Until that happens, speed isn't the SDLT600’s strongest feature, but its price makes it a good candidate for an update from other Quantum models.
In summary, each of these three units would be a solid investment capable of producing reliable backups and restores with unfailing regularity. Choosing the one that best fits your requirements can be an educational and also pleasant exercise. But whatever you do, don’t disregard the big picture and the upcoming generations of new tapes.
Ease of use (15.0%)
Overall Score (100%)
|HP StorageWorks Ultrium 960||9.0||9.0||9.0||8.0||8.0||10.0|
|Quantum Certance CL800||9.0||9.0||9.0||8.0||8.0||9.0|
|Quantum SDLT 600||9.0||9.0||9.0||8.0||8.0||8.0|
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