Choosing a data archiving strategy: Disk archiving vs. tape archiving

Data archiving is vital for most companies, but which is best for you, archiving to disk, tape or both?

Data archiving is a vital process for many data storage environments for several reasons. First, archiving data, either for long term or short term, allows a company to go back into archived files to retrieve a specific piece of data for customers or themselves. Second, data archives are often kept for a specific number of years for government regulations. With this in mind, companies generally have three data archiving strategies they can choose from: disk archiving, tape archiving or both. What are the pros and cons of each method? Which is better for your company? Or, is it best to use a mixture of disk and tape for your data archives?

There are several advantages and disadvantages to disk archiving and tape archiving, so many organizations often choose a combination of disk and tape, using disk for short-term archives and then transferring archived data to tape for long-term retention.

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"Everybody should use both," said Brian Babineau, senior consulting analyst at the Enterprise Strategy Group (ESG), Milford, Mass. "Your access requirements are going to vary, but in the first few years of your retention period, keeping it more accessible so you can get it back quickly is going to be critical. If you just need to keep it around and don't need to access it, tape becomes a logical choice for long-term archives."

Dean Flanders is the head of infomatics at Friedrich Miescher Institute (FMI), a biomedical research institute, and using both disk and tape for his data archives has served him well. For his short-term archives, he uses Oracle's Sun Storage Archive Manager to move data to disk. And every night, he archives his disk data over to his Spectra Logic tape system as well as an offsite tape storage facility.

"It makes sense to use a mixture of disk and tape," said Flanders. "Because you just have this security blanket knowing you have an extra copy of the data [on tape]."

So since combining the two technologies gives users the best of both worlds, what are the specific pros and cons of disk and tape?

Pros and cons of disk archiving

Disk archiving has several advantages. First, it's much faster to archive and restore data using disk than tape. Second, it's easier to index and search archives on disk. So if you wanted to go in and find a single email or file, that recovery process should only take a short time with disk. But storing large archives on disk can eat up a lot of unnecessary storage, floor space and energy, making it a costly process.

Pros and cons of tape archiving

Many companies archive data on tape for long-term storage, which requires less floor space and energy. Also, using tape for archiving can provide security, particularly if files are encrypted. Although administrators hope they never have to go through and search their tapes for information, they know the option is there if necessary. These factors make archiving to tape a smart option for large companies with a significant amount of data to store.

"Density-wise, tape has an edge," said Flanders. "You're looking at tape if you have more than 100 TB of data. [If you have] less than 50 TB of data, you need to evaluate if you really need the tape solution."

Price-wise, tape tends to be less expensive in the long run than disk.

"If you're storing things for 10 to 15 years, your total cost of ownership on tape will be less expensive than disk," said Babineau. "You don't have to go through migration. It's not spinning, those types of things. Tape is definitely cheaper."

It can take a considerable amount of time to identify the right tapes and the right place on the tapes where the data is located.
Nasser Mirzai
vice president of technologyTradeBeam Inc.

However, tape has significant disadvantages that many companies struggle with. Nasser Mirzai, vice president of technology at TradeBeam Inc. uses disk and tape to archive his data, but says he still runs into trouble when trying to restore from older tape media.

"Tape [cartridges] can get corrupted over time," said Mirzai. "They become unreadable, and also, the devices become aged and the [old formats] are no longer supported." According to Mirzai, this means you may not be able to recover that data sitting on tapes when you need to. Plus, e-discovery, indexing and search capabilities on tape systems are time consuming and frustrating. If your tape library from seven years ago was archived on a different backup software or operating system than what you currently have, you're in for a long haul of restoration and searching to try and extract one or a few files from your library.

"It can take a considerable amount of time to identify the right tapes and the right place on the tapes where the data is located," said Mirzai. "If you don't know [where your data is located], it becomes a nightmare challenge. You end up literally restoring as many tapes as you can, hoping that you'll find the missing needle in the haystack."

Facing tape archiving problems

For organizations who feel tape is the way to go for archiving, there are third-party solutions for making search and indexing easier.

For example, Index Engines Inc. recently rolled out a new program, the Tape Assessment Program, which searches and extracts files stored on tape archives. The Tape Assessment Program is able to search old tape libraries for a specific file, or files, and once those files are found, it can extract them without having to use the original backup software that was used to create those files.

According to Jim McGann, vice president of marketing at Index Engines, not having to use the old backup software saves both time and money for many companies in restoring necessary data files. "If a company has old tapes, their backup software may be an older version that's no longer deployed," said McGann. "So that makes it complicated, and restoration has all those issues associated with it. So now we have [users] that are getting their data off tape in hours and doing it themselves versus having to send it out to someone else to do the restoration."

The Tape Assessment Program supports most types of common backup formats, including the most widely used ones, including CA's ARCServe, CommVault, EMC Corp.'s NetWorker, IBM Tivoli Storage Manager (TSM) and Symantec Backup Exec and NetBackup. According to McGann, "90% of the market uses those platforms. And then as far as the physical tape, we support DLT, LTO and anything that can attach to a SCSI connection to connect to our appliance."

Another product that does similar tasks to the Tape Assessment Program is B&L Associates' Archived Data Manager (ADM), which is also capable of searching tape archives and retrieving those files without the original backup software.

Products like these can help alleviate many of the problems Mirzai encountered with his old tape archives.

So which archiving method is right for your company?

Overall, the data archiving strategy that companies choose depends on their storage requirements and legal policies. If you just need to store data for a short period of time, aren't storing hundreds of terabytes, and don't have long-term retention requirements, archiving to disk is your best bet. Or, if you are storing a large amount of data long term that you don't feel you need to access, but need to keep around for litigation purposes, archiving to tape is the cheaper and easier option. However, most companies have requirements that make them lean towards using both methods of archiving, and often this is the best way to go.

"I sleep much better at night with this approach that we've taken," Flanders said of his disk and tape combination for archiving. "Because I know I can bring everything back in every different disaster recovery scenario."

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