Mammoth-2, NetVault combo rips through backups

Posted on August 01, 2001

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OpenBench Labs makes short work of backing up 100GB per hour in a 19-inch rack.

BY JACK FEGREUS

Everyone in IT has heard of the "backup window," a term coined to define the time when the operations staff of the data center could back up systems without impacting normal operations. When mainframes were the platform of choice and single-disk units-such as an IBM 3350-approached 100MB, it was not unusual to see system backups being done manually between midnight and 6 a.m.

The Web changed all of that. Just five years ago people spoke in awe of a terabyte database. Now the mark of bigness is the petabyte. What does an ISP do when every customer wants its own 50MB Website? More often than not, the answer is to pop another 1U or 2U server into the rack along with a few storage appliances.


Figure 1 (left): The new version of NetVault was able to recognize the EXB-430 natively and make full use of the library electronics, including the bar-code scanning of tape cartridges.
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All of this demand leads to an acute need for high-capacity, high-performance tape backup at a reasonable price. Even if organizations could still afford to have large staffs mounting tapes all night long, they cannot afford to lose customers due to disasters, with no backups of crucial data. Yet there is a light at the end of the tunnel: New tape drive technologies such as LTO, DLT, and Mammoth-2 deliver high-capacity, high-performance backup at an affordable price and, when installed in robotic libraries, these drives can solve most enterprise backup problems.


Figure 2: In addition to performance enhancements, the new version of NetVault provides for enhanced logging of performance data, as seen in this drill-down of one of our backup tests, which provides both average backup throughput and compression results.
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Unfortunately, that's not enough for most ISPs and ASPs. When leasing data-center floor space by the cage, a gigantic robotic library is about as useless as an anchor for the Titanic. For these users, rack density and power consumption are of crucial concern. For this reason, we decided to look at Exabyte's new Mammoth-2 (M2) tape library, the EXB-430.

The EXB-430 measures 8.65 inches high by 17.25 inches wide by 24.10 inches deep and weighs 76 pounds with four tape drives installed and no cartridges. It's designed to be installed in a 19-inch rack-mount cabinet, but it can also be used as a desktop unit. Don't let that small footprint fool you: This is a full-featured robotic tape library that can pack 1.8TB of uncompressed data on tape, which translates into 3.5TB of real data-assuming a nominal 2X data compression ratio and 225m cartridges.

The library has space for 30 M2 Advanced Metal Evaporative (AME) cartridges, which are spread over two 10-slot magazines and 10 fixed slots. There's an entry/exit port on the front of the library to add and remove cartridges without interrupting the operation of the library. The AME cartridges use Exabyte SmartClean technology, which combines normal recording media with a segment of head cleaning material.


Figure 3: Performance of both the EXB-430 and NetVault 6.0.3 was exceptional. Native throughput for the Mammoth-2 drive is specified at 12MBps. Using the obltape benchmark and writing 128KB records, we sustained a throughput rate of 22.1MBps. With NetVault, our backup throughput averaged 18.7MBps. Instantaneous rates, however, were as high as 29MBps. With two simultaneous backups taking place, average throughput rose to 30.1MBps.
Click here to enlarge image

The library has robotics to automatically move cartridges between the slots, entry/ exit port, and drives. The robotics can be equipped with a bar-code scanner that can read labels on the cartridges to maintain an inventory of cartridges. In the absence of a bar-code scanner, the library must mount each cartridge on initialization and read its header to determine the cartridge's contents. This is a long process, even with only a few tapes in the library.

While the true power of the EXB-430 is in its robotics, the library cannot attain its true potential without good backup software. To test the EXB-430, we used Net Vault backup software from BakBone Software. We used a very late beta version of NetVault, v6.0.3, which can natively manage the EXB-430's robotics. The EXB-430 can also emulate earlier Exabyte tape libraries such as the EXB-210.

For our backup tests, we used a standard set of files taken from our own servers. This collection of files allows us to test the library and tape drives in a real-world situation. In today's terms it is a relatively small data set-just 4 GB-but large enough to exercise the tape drives sufficiently. Most importantly, it is made up of many different types of files, including images, text documents, and program files. This mix allows us to get a realistic compression ratio for our tests.

As with our previous test of the Exabyte X80 library (see InfoStor, February 2001, p. 64), we set each drive's buffer to 30,721KB. With the new version of NetVault, we were able to increase the size of a data block from 64KB to 128KB. We also adjusted the size of the buffer in our obltape benchmark to handle 256KB data blocks. All that was left was to measure the performance of the NetVault/EXB-430 combo.

We expected very similar results to what we had measured with NetVault 6.0.1 and the Exabyte X80, with a jump of maybe 5% to 7% in performance. However, what we measured were performance increases that in some cases exceeded 25%. On a single backup process, we were able to average 18.7MBps, which represented a 7% boost in throughput.

What was really eye-popping was the rate at which the new version of NetVault restored our saveset. The restore blazed away 32% faster than before and clocked in at 18.5MBps. Finally, we measured the scalability of the EXB-430 by running two backups in parallel: We saw aggregate throughput jump to 30.1MBps.

If you were a computer operator in the old days, this article might bring back fond memories. Our memories are not so fond, consisting mostly of staying up all night to mount reel-to-reel tapes every time the console buzzed at us! Don't pine for the old days. Instead, get yourself a robotic tape library like the EXB-430 and do the backups you should be doing without losing sleep or disrupting your users.

Jack Fegreus is editorial director at Open (www.openmagazine.net) in Newton, MA.


OpenBench Labs scenario

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Under examination


  • Tape library automation hardware and software for a rack-mount environment

What we tested


  • Exabyte EXB-430 tape library (www.exabyte.com)
  • NetVault v6.0.3 backup software (www.bakbone.com)

How we tested


  • Siliconrax-Sliger Rax2100 Web server running Red Hat Linux v7.0 (www.siliconrax-sliger.com)
  • QLogic QLA12160 Ultra160 SCSI controller (www.qlogic.com)
  • OpenBench Labs obltape v1.1 benchmark
  • OpenBench Labs 4GB backup file set

Key findings

  • NetVault sustained equivalent throughput on restore operations as on backup.
  • With multiple backups running simultaneously on two drives, throughput rose by 61%.


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