D2D2T – the complete backup and archiving solution

 

By McClain Buggle, Product Manager for Disk, Tandberg Data.

 
Although tape has been the preferred medium for backing up computers and archiving data for decades, today’s more sophisticated solutions combine tape with disk. 

 
Tape cartridges are inherently cheaper than disk, while tape’s portability makes it easy to store data away from the computer system.  Tape is also the most reliable medium for long-term archiving.

 
Disk is far faster, delivering quicker backups and restores thanks to its ability to access data randomly instead of sequentially. This makes it easier to consolidate storage.  However, disk costs more and has the potential for hardware failures with subsequent data loss. While disk-to-disk (D2D) backup solves several storage issues, it is not a complete backup and archive solution and leaves critical corporate data at risk.  

 
In most environments, disk backup is a “nice to have” while tape is a “must have.” But the best answer for organisations requiring fast backups and restores is to mix disk and tape. Disk-to-Disk-to-Tape (D2D2T) is the combination of Disk-to-Disk and Disk-to-Tape.  In essence it takes the best from both worlds. And if speed of backup is essential, D2D2T is the only complete solution - tape provides low cost archiving, while disk provides increased performance and accessibility. 

 
The advantages of D2D2T lie in quick backups and restores that reduce network bandwidth issues; reduced backup window concerns; consolidated storage; portability of tape that provides security against fire, theft, viruses and natural disaster; and tape providing a cost-effective solution for long term archiving.

 
In D2D2T, data is first copied to a disk storage system then copied again to a tape backup system. This expedites backup first by copying data directly from one tier of disks to another, then enabling tape backup as a separate operation.

 
The data resides on the second tier disk until it is ready for long-term archive, which allows it to serve both as a staging area for the tape backup and a holding area for quick restores. The idea is to back up from the production disk to a backup disk as quickly as possible. Once the Disk-to-Disk (D2D) portion has finished, files can be backed up to tape at a more comfortable pace without impacting the performance of the primary storage space.  The additional disk stage will add cost, but for some customers speed is vital.

 
Most disk solutions can be used in D2D environments, including NAS Boxes, RAID Systems,
Appliance Servers, File Servers, and Virtual Tape Libraries. The disk can be implemented as
direct attach storage, but most commonly it is used as a target on the network.

 
While the price is lower, so is the reliability and performance. The MTBF for hard drives may be higher than tape drives, but a failed hard drive results in lost data whereas a failed tape drive does not, since data resides on the tape media. In fact the more hard disks that are added to the storage pool the higher chance of failure, where the opposite is true for tape.

 
Once a second tier of disk has been implemented, a third-party backup application is used to copy data from production servers to the second tier disk where it is available for

restore. When it is time for off-site backup and archive, the software copies data to tape.

Some disk setups connect a tape device directly to the disk solution, allowing data to be migrated directly to tape without impacting the network.

 Most third party backup applications were designed and optimised to write to tape. As the applications evolved, support was added for disk but the performance increase was marginal. To solve this problem, virtual tape library (VTL) software can be added to the mix. VTL software presents the second tier disk as though it were tape, often by emulating the tape device. In most cases VTL software can transfer data faster than typical backup applications, but it’s also another application to purchase, integrate, and maintain.

 
As organisations become more global, the time available to perform backups (backup window) continues to shrink, but D2D2T is well suited to address this challenge.  With more and more pressure on IT departments to protect data and make it readily accessible, companies are looking for more complete solutions to traditional tape backup and restore.  With a properly designed D2D2T solution, IT departments can spend their time working on other critical issues.  Tapes will be ready for off-site storage and restores can be done quickly during the day, allowing business to continue uninterrupted.

 

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