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Big three apps adjust to disk-based backup

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And it took three weeks for Arun Sondhi, the storage management group lead at a Milwaukee manufacturer, to integrate NetWorker with Sun Microsystems Inc.'s StorageTek ACSLS Manager. Backing up his servers behind a corporate firewall required the purchase of another NetWorker server because opening 25,000 TCP/IP ports on the firewall posed a huge security risk to the organization. His "reliance on backup software has become so big that if it sneezes, the CIO hears it," says Sondhi.

In response to user requests for new features, EMC, IBM and Symantec are:

  • Increasing their support for faster backups and recoveries
  • Enhancing support for encrypted data
  • Offering better ways to protect remote offices
Disk-based backup
Backing up to disk dramatically improves backup times, usually in the 30% to 50% range or greater. Aaron Mathes, chief operations officer for information services at Liberty University in Lynchburg, VA, finds that disk provides him with a higher degree of confidence that his backups are completing successfully. "Disk has had an exponential impact," he says, adding that he backs up 90% of Liberty University's 4TB of data to a disk cache.

The EMC, IBM and Symantec products all include the ability to manage a disk cache (it's an optional feature for NetWorker), a disk volume where data is initially parked before being moved to tape. Disk

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caches can be shared drives on an Ethernet network or a Fibre Channel (FC) SAN drive owned by the backup server. When using a disk cache it's important to:
  • Select volumes large enough for each server to keep a week's to a month's worth of backups online to expedite recoveries. NetWorker 7.3 has a wizard that assesses the size of each server's backup and required retention period, and helps administrators select a disk volume large enough to meet those requirements.


  • Determine what copies of the disk backup need to be written to tape and when. For instance, if a server does incremental daily backups and full weekly backups to the disk cache, you may opt to copy only the full weekly backups to tape to conserve tape and schedule the copies during low-traffic backup times to lessen their impact.


  • Use a watermark, which deletes or transfers backups from the disk cache when a certain level is reached, for example, 90% of disk capacity.
There are three basic ways--high watermarks, time based and manual--in which vendors allow users to manage disk cache threshold levels, although each feature is not in every program. Another major way traditional backup programs are changing is in their support for virtual tape libraries (VTLs). A VTL presents its disks as virtual tapes, and its disk array FC or iSCSI ports as virtual SAIT, SDLT or LTO tape drive images to the backup software. VTLs are easier to implement in the sense that backup software treats VTLs like physical tape libraries--it will detect and manage virtual tapes and tape ports the same way it does with tape libraries. But users may pay extra for VTLs; they cost more on a per-megabyte basis than similarly configured generic disk arrays, and EMC and Symantec charge an additional software license fee to manage VTLs.

Backup software vendors license their VTL software by virtual tape ports or VTL capacity. Symantec initially licensed NetBackup for VTLs the same way it did for a tape drive--by each virtual tape drive. Because a company may use tens--if not hundreds--of virtual tape drives, this licensing approach quickly becomes cost prohibitive. For instance, using Symantec's old model, licensing for 12 virtual tape drives on a 20TB VTL cost $60,000. Symantec now offers NetBackup licensing based on total VTL storage capacity. With the new model, the licensing cost for the 20TB VTL is only $20,000 ($1,000 per VTL terabyte); however, users still need to monitor VTL capacity growth to control future costs.

In addition to having to adjust to different licensing costs, some VTL users are finding that their backup bottlenecks are moving from the tape device to the server. As the speed of backups increase, the VTL puts more demands on the server to ship data to it faster. Ian McLeavy, manager of global enterprise storage at Black & Decker in Baltimore, implemented five EMC VTLs that lowered his NetWorker backup times from 11 hours to seven hours. But because of the increased CPU activity, says McLeavy, "the backup bottleneck has moved to the server."

This was first published in April 2006

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