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What's driving secondary storage?

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There are many factors that contribute to the feasibility of adding secondary storage in a tiered architecture:

Growing data stores on primary storage
Continuing high prices for high-end storage vs. lower priced ATA and Serial ATA (SATA) disks
Greater capacities available with ATA/SATA disks
future generations of SATA will match or surpass Fibre Channel performance
Backup inefficiencies using tape
Regulatory compliance
The need to better control data management
Business continuity/disaster recovery
Availability of low-cost connectivity
Virtualization makes it easier to mix arrays and add lower cost disks

Making data safer
Today, secondary storage is most often used to bolster data protection activities. Traditional backup to tape has significant shortcomings, most notably the time required for daily and weekly backups and the difficulties of recovering archived data from tape. With far greater ease of use and faster access speeds, secondary storage is an ideal remedy for backup woes.

Industry statistics support the practicality of inserting some form of disk-based backup into typical backup scenarios. Most analysts say that approximately 75% of data that needs to be recovered is new, having been accessed or created within the last 72 hours. They also note that approximately 90% of recovered data is two weeks old or last accessed within that period. "Statistically, most people don't ever recover data after 21 days," says ESG's Hurley.

Those statistics help make a good case for using secondary storage. Because of the low cost of secondary storage, some companies have opted to eliminate tape altogether and back up directly to disk. Secondary storage system prices are competitive with many tape backup devices, albeit disk-based systems don't provide the kind of portability that tape does for storing backup copies off site. D2D backup does, however, compensate with speed--for both backing up and recovering data. Transportability of backup disks is getting more attention, with new products such as Spectra Logic Corp.'s Spectra RXT, a removable tray that holds up to 1TB of SATA disks in a ruggedized case that can be mounted in the company's Spectra T950 tape library.

At MIT's Lincoln Laboratories, Lexington, MA, the storage group uses low-cost Winchester Systems ATA arrays to speed the backup of an Oracle database. "By copying the files to the ATA array, we can cut down the backup time significantly, from 18 hours with tape to 1.5 hours with disk," says John Riopel, systems manager.

Such D2D backup is becoming increasingly attractive as the cost of ATA disk drives steadily drops. The economics of ATA make a big difference to storage managers like Tom Schultz, chief engineer at the Enterprise Imaging Group of Partners Healthcare, Boston. "I can get a 1TB ATA disk array from a midtier vendor for $4,000. An FC SCSI array would cost as much as two to five times more," he reports.

Partners is able to buy sufficient ATA disk to store three years worth of compressed images (approximately 25TB of data) before it is archived to tape. With Fibre Channel SCSI, the imaging group could only afford to keep 18 months of data online before going to tape.

Carol Braden, manager of data management for Trilegiant Corp., a membership club marketing firm based in Norwalk, CT, recently installed ATA disks in the company's EMC Corp. CX600. The new disks will be used to do point-in-time backups of an Oracle database using Oracle's Recovery Manager. "Backup will run faster and have less impact on your users," says Braden. "Any restores you have to do for local outages will be a lot faster because you don't have to go to tape." Trilegiant's setup uses the ATA disk as a staging area, with the backup data on disk eventually moving to tape.

The proliferation and enhancement of snapshot technologies also gives secondary storage a boost. This provides the dual benefit of quicker initial backups and easy access to saved data, while easing the constraints of traditional backup windows. Snapshot software that works across vendor and product lines is widely available, making it easier to mix and match storage devices according to function. Frequent snapshots of production data can be saved on secondary disk before backing up the data to tape for long-term archival. This makes it easy to satisfy data restore requests that typically occur when the data is still fresh, and the backup to tape process can run at any time without hindering operations.

Even without using snapshots, secondary storage can measurably speed up backups. Aetna, the insurance giant based in Hartford, CT, is using disk pooling and NetBackup to stage its backups for its Unix environment. Aetna uses approximately 10TB of what Nancy Guerin, head of storage management for mainframe and Unix servers, describes as "non-enterprise class" storage on an EMC Clariion, although it's still part of its overall FC environment. "Looking at the price differential," says Guerin, explaining the company's decision to eschew ATA or SATA disks, "it wasn't worth giving up some of the reliability points." Guerin adds, however, that they will consider ATA disks when they look at e-mail and database archiving.

This was first published in August 2004

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