| OPENBENCH LABS SCENARIO |
Under examination
Tape library automation hardware and software
for a rackmount 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 controller
www.qlogic.com
OpenBench Labs obltape v1.1 benchmark
OpenBench Labs 4-GB 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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Everyone in IT has heard of the "backup window." It was coined to define the time when the operations staff of the data center could backup the systems without impacting normal operations. When mainframes were the platform of choice and single-disk units-such as an IBM 3350 DASD-approached all of 100 MB, it was not unusual to see system backups being done between midnight and 6 a.m.
The process was more often than not a manual one, with a system operator being prompted to mount the correct tapes in sequence. Nonetheless, this "backup window" was usually big enough to do any backups that were required. The need for high-capacity, high-performance tape drives and robotic tape libraries only existed at the biggest corporations: Smaller companies simply made do with slower, lower-capacity standalone tape drives.
The Web changed all of that. Forget servers; desktop PCs now routinely sport 20-GB, 30-GB, or even 50-GB disk drives, and lots of them. Whereas just five years ago people spoke in awe of a terabyte (1,000 gigabytes) database, the explosion of e-commerce, CRM, ERP, and business-intelligence software has made terabyte databases commonplace. The mark of bigness in the online explosion is the petabyte (1,000 terabytes!).
So it's not surprising that the Internet revolution has pushed ISPs to the edge. What do you do when every customer wants its own 50-MB Web site? More often than not, the answer is to pop another 1U or 2U server into the rack along with a few storage appliances.
The Internet has also shrunk the "backup window," for many enterprises that are now doing business on a global scale with 24x7 computer operations. For good measure, add the growing trend towards outsourcing and ASPs, who aggregate data of many customers.
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.
These tape drives, installed in robotic libraries, can solve most enterprise backup problems. Unfortunately, that's not enough for most ISPs and ASPs. When leasing your 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" high by 17.25" wide by 24.10" deep, and weighs 76 pounds with four tape drives installed and no cartridges. It's designed to be installed in a 19" rackmount 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 1.8 TB of uncompressed data on tape, which translates into 3.5 TB of real data-assuming a nominal 2X data compression ratio and 225-meter 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 is an entry/exit port on the front of the library where cartridges can be added or removed 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 to make each cartridge self-cleaning.
Internally, the EXB-430 uses two wide, low-voltage differential SCSI controllers, one for the tape drives and one for the robotics. Up to four M2 tape drives can be installed, with each drive having its own cooling fan. An LCD display on the front panel of the library allows you to select configuration options, monitor operations, and control robotics manually. We used the front panel to manipulate the robotics and found that, although this method works, you are better off using backup software to manage the robotics.
The library has robotics to automatically move cartridges between the slots, entry/exit port, and drives. The robotics can be equipped with a barcode scanner that can read labels on the cartridges to maintain an inventory of cartridges. In the absence of a barcode 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. Take our advice: Get the model with the barcode scanner-it will save you time and frustration.
As an option, the library can have an Ethernet connection and use Exabyte's Library Monitor software to check the library's status, create diagnostic listings, and upgrade firmware. Our evaluation unit did not have this option installed, so we were unable to
test its functionality.
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 NetVault 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, allowing you to examine the operation and status of the library, tape drives, and tape contents. To lessen the need for the
latest in backup software, the EXB-430 can also emulate earlier Exabyte tape libraries, particularly the EXB-210 and EXB-440.
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-being 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, we set each drive's buffer to 30,721 KB. With the new version of NetVault, we were able to increase the size of a data block to 128 KB from 64 KB. We also adjusted the size of the buffer in our obltape benchmark to handle 256-KB 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 5-7% in performance. What we measured were performance increases that in some cases exceeded 25%. On a single backup process, we were able to average 18.7 MB/sec, 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 18.5 MB/sec. Finally, we measured the scalability of the EXB-430 by running two backups in
parallel: We saw aggregate throughput jump to 30.1 MB/sec.
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.
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