Efficient backup
Tape libraries are commonly used in large organisations for backup and archiving, but the growing volume of data and the lengthening of the business day make it hard to complete overnight backups in the time available. The “obvious” solution is to add another library so that backup can be done in parallel. While tape has a very low incremental cost per gigabyte, a new library is a substantial investment and also has a relatively low utilisation.
Organisations are now backing up to disk to achieve significantly greater performance, but integrating that approach with an existing backup strategy can be difficult. Quantum has addressed these problems with the DX30, a disk-based backup unit that emulates a tape library and therefore works with current backup software and procedures, yet has a throughput of 80MB per second.
Once the primary backup is complete, the data can be spooled off to tape at leisure. And when a backup file must be recovered, there’s a good chance that it will still be on the DX 30 as 96 percent of all restores are performed within 90 days, according to Quantum’s product marketing manager Mike Sparkes.
Although data is stored in tape format rather than individual files, the DX30 is amenable to synthetic full backups, he says. This involves performing full backups at infrequent intervals interspersed with frequent incremental backups, and relying on software that’s smart enough to restore the most recent versions. That strategy is complicated when dealing with tapes, involving lots of tape swaps in order to restore a complete set of files, but works well in terms of storage efficiency and ease of restoration with a disk-based backup device.
With a price tag in the vicinity of $110,000, you wouldn’t regard the DX30 as a cheap alternative—but if you’ve maxed out the throughput of your existing library, a DX30 could save you spending $380,000 on an additional library with equivalent performance, so the term “relatively inexpensive” may be appropriate. If the 3TB capacity isn’t sufficient for your needs, the first quarter of 2003 will see the release of the DX100 with 10-15TB capacity and throughput in excess of 100MB per second.
“As applications grow, they drive more and more [batch] jobs that need to be done,” says Terry Crawford-Smith, channel sales director at BMC Software. He points to the experience of a Victorian power utility where overnight backups took around nine hours to process. Various reports and other batch jobs had to be run first, so if there were any delays the backup might not finish before staff arrived the next morning.
The obvious solution was to “throw more hardware at the problem,” but instead the organisation chose BMC’s SQL-BackTrack, which provides object-level backup and recovery. The combination of selectively backing up new or changed data and compressing it slashed backup times to around one third, Crawford-Smith says. Apart from the operational advantages, the organisation reduced its tape bill by $50,000 per year. The software was used in conjunction with CONTROL-M, another BMC product, which provides smarter logic, he adds, running jobs in parallel where possible and automatically restarting failed jobs.
This idea of a storage hierarchy can also be seen in other companies’ offerings. Rather than trying to keep everything on expensive high-performance storage, older (or less important) data can be migrated to slower, cheaper devices such as ATA disks, nearline storage such as tape libraries or DX30-style units, or even offline storage requiring operator intervention.
“Anyone that’s got large amounts of data that isn’t used very much after the first week or so” can benefit from hierarchical storage management (HSM) says Joan Tunstall, marketing manager at StorageTek Australia/New Zealand. While early targets for the technology included audio-visual material and scientific data, “it’s becoming more mainstream, driven by the fact that everyone’s experiencing a data explosion,” she says. One clearly mainstream application for hierarchical storage is e-mail. Mail volumes continue to grow, but requiring users to manage their own mail is a real time-waster, and also risks the inadvertent deletion of legally critical messages. “You get a clear payback” by applying HSM to e-mail, Tunstall says, because the productivity costs can be readily quantified. While she cites the annual cost of each mailbox at $5000 without HSM and $1200 with it, she admits “business cases built on individual productivity [depend] very much on what the organisation is prepared to concede.” Another example of the application of HSM to e-mail is Veritas Storage Migrator for Exchange, which migrates e-mail attachments from disk to tape.
If an organisation is facing data growth that in excess of storage budget growth (after allowing for price/performance improvements), HSM should be considered, says Tunstall.
