Let's go to the tape

But the fastest tape libraries use disks instead of tape

The RFP Checklist: Look and Listen

Selecting the best virtual tape library solution requires a close look at existing backup systems and consideration of future storage needs. Here are important questions to answer before picking a solution.

Does it include technology for migrating from the VTL to tape? Is this process manual or automatic, based on first-in, first-out or other policy?

Does the VTL provide a virtual representation of the physical tapes in use or just some other model of tape? If it does not virtualize exactly the same tapes, backup processes should change.

Does the solution work with existing backup software without additional configuration or modification?

Will the VTL run in parallel with the tape backup or will it be disk-to-disk-to-tape?

What is the age of the files that typically need to be restored? Size the VTL accordingly. Build a graph that shows how deeply into the past you have to reach to accommodate most of the recoveries. You want to eliminate the need to restore from tape as much as possible.

Is the solution a complete system, or are the hardware and software separate?

What type of encryption does the product include? Does it encrypt on the disk or only when it goes to tape? Is the encryption done in hardware or software?
Remember, hardware encryption is faster and doesn't consume the resources needed for backup.

What level of compression is being used? Is the level of compression the vendor is proposing realistic for the types of files in your system?

Does the compression take place in the hardware or software? If it is software compression, it will slow data throughput.

Can the VTL virtualize your existing volumes or tape libraries?
Has the VTL been tested with the backup software you are using?

The good news is that storage prices have fallen dramatically in recent years. The bad news is that this just encourages the purchase of more storage, compounding backup and restoration problems.

"We have a couple of large servers that hold about 1.5T of data," said Andrew Ferguson, enterprise operations manager at Brookhaven National Laboratory. "Doing a full backup on it would take days."

The laboratory has about 160 servers in its administrative data center, along with a storage-area network fabric. Two years ago, to address the dual issues of backup and restoration, Brookhaven installed an S2100-ES virtual tape library from Sepaton Inc., of Marlborough, Mass. The laboratory uses EMC Corp.'s NetWorker to back up about 45T of data from the servers and the SAN. Most of it goes to tape, but the most critical data goes to the Sepaton VTL. Backing up a 1.5T server now takes less than 22 hours.

"We can start it on Friday night, and it is done sometime Saturday, which is perfect," Ferguson said. "We recently restored that data to another server in a 24-hour window."

Tossing the tape

Tape has never been an ideal backup technology, but it has had one overwhelming advantage: price.

That was certainly the case in 2000, when primary disk storage cost $80 per gigabyte, or 200 times the 40 cents per gigabyte cost for tape, said Simon Robinson, senior analyst at market research firm the 451 Group. By the end of 2005, the cost of tape storage fell to only 12 cents per gigabyte. Although that 70 percent drop in tape price is impressive, it does not compare to the way disk prices have decreased. By the end of 2005, primary disk storage cost $2.50 per gigabyte, and secondary drives were a mere 50 cents per gigabyte. Although disk storage remains somewhat more expensive than tape, the price is close enough that the advantages of disk storage ? speed, administrative costs and reliability ? may tip the scales for some users.

Although disk storage systems have grown more popular, many organizations still have a significant investment in tape backup systems, including the backup software and procedures. This is where VTLs come into play. VTLs are disk arrays that appear to the backup software as tape drives.

"The big value that VTL delivers is it allows you to operate with precisely the same processes you have always operated with," said Mike Karp, storage practice leader at Enterprise Management Associates. "But in place of physical tape, you have a virtual tape."

This allows an organization to migrate part of its backup processes to disk while continuing to use tape for the rest.

VTL advantages

Switching from tape backup to a VTL offers organizations several advantages. The biggest of them is speed. Backing up data to disk is much faster than backing it up to a tape drive. This is especially critical as lengthening backup windows start intruding into peak operational periods.

"The backup window was becoming increasingly larger, and many backups ran into the next business day because of sheer volume of the data," said Sheetal Sood, New York City Department of Transportation systems manager.

Setting up a 25T EMC Disk Library 710, a process that took less than a day, brought backup windows back under control.

"Any other solution would have caused us to make many changes in the backup software configuration," Sood said. "But with the EMC Disk Library, we did not have to make any changes; the EMC solution appeared to the backup software just like any other tape library."

Chris Ferko, network operations manager for the city of Tucson, Ariz., reported similar results. When backup windows started extending into business hours, the city installed a 4T Hewlett-Packard 6518 Virtual Library System. "By implementing the VTL, we were able to reduce our backup window to two hours from in excess of 10 hours," he said.

But speed is not the only consideration in backing up data. Data is backed up so it can be restored, and disks are superior to tape in this area, too. Recovering data from tape is a cumbersome process of pulling and loading the right tape and then scanning for the required file.

Customer service

That, of course, makes a big difference in service levels.

"More rapid and reliable recoveries boost customer satisfaction," Karp said. "You can really make IT shine, because now people aren't waiting for hours or days to get a recovery."

Plus, with tape there is always the question of whether the data can be reliably backed up and restored at any speed.

Nightly backup failures are a common occurrence, and there is the question of whether data will be recovered properly from tape. This is especially critical when rebuilding a crashed server, such as the 1.5T of data Ferguson recently restored.

"When you have that much on a server, you always fear that one bad tape is going to blow you out of the water," he said. "With the VTL, you know you can just start the restore and go home. You don't have to worry about it."

There are two basic approaches to implementing a VTL. One can purchase the disk array and VTL software separately or buy them as an integrated system. "The advantage to a preconfigured system is that IT doesn't have to get into the system configuration business," Karp said. "On the other hand, there might be a price penalty for that."

Each of the customers interviewed for this article had selected a preconfigured system, and installation took less than a day.

On the grow

Given the advantages VTLs offer, coupled with the rapid price drops for disk storage, market research firm IDC forecasts that the VTL market will double to $1.4 billion by 2011, with VTL capacity showing a sevenfold growth during that same period. But the long-term prospects for VTL are uncertain.

"Although we don't think VTLs will disappear anytime soon (i.e., in the next two to three years), in the longer term they will become less important as the nature of backup changes," Robinson said. "VTLs are only popular because backup applications don't know how to talk better to disks."

Drew Robb is a freelance writer in Los Angeles.

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