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BEST OF BOTH WORLDS

From STORAGE Magazine Vol 8, Issue 06 - October 2008

DISC-TO-DISC-TO-TAPE - D2D2T - IS A KEY FACTOR IN THE STRATEGY OF SO MANY BUSINESSES WHEN
IT COMES TO MANAGING THEIR DATA. HERE, WE EXAMINE ITS ROLE IN TODAY'S STORAGE INDUSTRY

Sometimes called 'virtual tape', Discto- Disc-to-Tape (D2D2T) takes advantage of the speed of disk by providing a short-term buffering or staging area for backup data, prior to the data being written to tape.

Most importantly, D2D2T allows businesses to execute a strategy that exploits the best attributes of disk and tape when creating data protection solutions, providing businesses with a viable strategy of data protection that addresses two core aspects of data protection - business continuity and disaster recovery.

Disk-to-disk backup systems allow disk to be the initial target for the backup image in a data protection environment. "For applications that require quick restore/ retrieval times, disk is the better choice," claims Steve Mackey, area sales director, Northern Europe, Quantum.

However, not all applications have such a need for speedy retrieval access requirements. Integrating disk with current tape-based backup infrastructures should always be evaluated to provide quick restores for those applications that demand it. A tiered storage architecture offers the best of both worlds in a D2D2T environment, Mackey argues - ie, fast retrieval from disk for frequently accessed data, and cost-effective and slower access storage for long-term archive.

TIERED SOLUTION

"More often than not, we find that a tiered storage architecture, including disk at the primary level and tape at the backend, best suits our customers," he says. "Data is kept on disk for a short period of time and then migrated to lower cost tape for the duration of its retention period. With the use of a VTL, for example, storage administrators can implement disk without requiring changes to their existing processes, as this form of disk-based backup presents itself as tape."

Appropriately, using tape for storage can also significantly reduce power consumption, as well as the total cost of ownership, making the data centre more environmentally friendly and freeing up the limited supply of power for use elsewhere. "Another option in the field of D2D2T is to implement data management software to store - more data at a lower cost. For long-term data storage, data management software automatically moves data between different storage tiers to reduce costs and protect content. Data locations can be virtualised, so that any file can easily be accessed for re-use, even if it resides on tape."

According to Mike Walters, consulting systems engineer, NetApp, it is finding that more businesses do not want to rely solely on tape as their first path to data protection. Customers are now looking to disk to accelerate the business continuity and disaster recovery processes to make them more reliable, and there are two clear approaches that can be taken.

"The first option is to deploy a virtual tape library (VTL). VTLs are designed to integrate into existing environments, as they simply 'look like tape' to the backup server. Being disk, however, they have significant performance and reliability advantages over traditional tape mechanisms, as well as being simple to manage. In addition, the random-access nature of VTL disk means that recoveries can easily co-exist with backups, removing the risk of possible device conflict and providing much greater flexibility in day-to-day use."

In a D2D2T architecture, a VTL will be deployed to push tape farther away from being a primary recovery mechanism. "It is therefore important for customers to examine how easily VTL solutions can integrate with tape," he says. Do they keep costs down by maximising the use of physical tape and can they take the tape processing away from the backup server to improve performance? "In particular, what type of management processes are needed to ensure that the VTL performs as expected? It is rare for companies to have idle administrators and, if a VTL is used in conjunction with tape, it is essential that it is easy to manage and self-tuning."

INTELLIGENT INTEGRATION

The second approach, he suggests, is to deploy solutions that integrate more intelligently with primary storage. These types of solution only move changed data from the primary disk to the secondary disk, so instead of an incremental backup taking, perhaps, 10% of data across on a daily basis, the customer only has to replicate a much smaller amount: 0.1% to 1% of data - a huge saving in disk and/or tape costs.

Certainly, D2D2T has become one of the established and recognised methodologies for executing effective and watertight business continuity and disaster recovery, especially when it comes to the SME and departmental sector.

"And it's easy to see why," states Marije Stijnen, director of corporate marketing, Tandberg Data. "IDC [in its research and analysis paper, 'Worldwide Storage 2008 Top 10 Predictions: New Paradigms'] reports that storage capacity is growing more than 60% annually, pressuring companies of all sizes to increase their storage capacity at a similar rate."

It is widely accepted that users like, and require, the blistering speed, instant access of disk where data is effectively accessed, located and stored for a defined period of time before being archived onto tape, she adds. "Users continue to like tape, because of the cost, familiarity and the ability to offsite archive in secure storage."

Job done. Or is it the full picture? Tandberg Data doesn't believe so. "In today's more cost conscious and power conscious environment - and faced with prolific data growth rates - tape is enjoying a resurgence as the primary backup methodology, as the cost of running virtual tape (disk) versus tape falls under the spotlight," it states. "Extensive studies continue to be carried out by both camps, the most recent of which by the Linear Tape-Open (LTO) Programme highlights that companies that use hard disk-only storage are now looking to incorporate tape storage technology as part of a tiered storage infrastructure to support backup and archiving."

Businesses want faster access to their information, naturally enough, and this is proving to be a catalyst for the increased adoption of disk-based storage where tape has been previously used.

As Mike Walters of NetApp points out: "Technologies such as VTLs are becoming commonplace in today's data centres and multi-tiered storage practices are proving beneficial, in terms of cost savings and efficiency. D2D2T storage solutions have a clear and effective role in today's storage industry, and provide many real benefits to data protection, business continuity and disaster recovery."