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VOYAGE OF DISC-OVERY

From STORAGE Magazine Vol 6, Issue 8 - October 2006

Is disc-to-disc-to-tape (D2D2T) the way forward for those swamped by their data storage challenges? Or is it more complex than THAT? is media usage dictated according to end user circumstance, priorities … and budget? Editor Brian Wall has been finding out

The marriage of disk and tape has not always been a happy one, often characterised by a heated debate over which medium is 'best' for backup. With the decreasing cost of disk, disk-based backup is now highly feasible and offers the advantage of much more rapid restore. However, the need - and indeed statutory obligation, in many instances - to retain more and more information for longer periods of time means that a pure disc solution is impractical. Many organisations now favour 'a stratified solution', where they back up to disk first as an intermediary and then remove that to tape thereafter.

Disk-to-disk-to-tape (D2D2T) is an approach to computer storage backup and archiving in which data is initially copied to backup storage on a disk storage system and then periodically copied again to a tape storage system (or possibly to an optical storage system).

Traditionally, many businesses have done back-up directly to relatively inexpensive tape systems. However, for many computer applications, it's important to have data immediately ready to be restored from a secondary disk, if and when the data on the primary disk becomes inaccessible (for example, if the server were to fail). The time to restore data from tape would be considered unacceptable. On the other hand, tape is a more economical alternative for long-term storage (archiving). Since it's also more portable, tape is often used for off-site backup and restoration, in case of a disaster.

Disk-to-disk-to-tape is often used as part of a storage virtualisation system. In such a system, data that is more likely to require restoration from a backup device may be kept on an on-site or off-site disk storage system. Data that has less value over time, such as email, may be migrated on a set schedule to tape. The storage administrator can express a company's needs in terms of storage policies, rather than the physical devices to be used.

According to Robert Schaefer, chief executive officer, Breece Hill, the introduction of disk and tape into a company's data protection architecture need not be an either/or situation. "While tape is the most cost-effective media for long-term storage (archiving), restoring data from tape is time consuming and backups are often difficult to manage," he says.

"Disk-only systems offer a viable alternative. They are relatively fast when restoring lost files and eliminate the need to search through a multitude of tapes. Still, disk-only solutions are more expensive than tape and are not portable for offsite storage. In addition, disk-only solutions do not offer disaster recovery capabilities."
The unification of these two technologies into one solution has enabled the creation of superior data protection capabilities previously available only to large companies and enterprises. Disk-to-Disk-to-Tape solutions make it possible to offer complete backup/recovery and archive management solutions for small to medium businesses (SMBs) with unsurpassed reliability, performance, capacity and innovation, he adds.

"While many SMBs understand the importance of having a data protection solution, their unique requirements necessitate systems that are easy to own, manage and operate. These companies require the right functionality and performance and minimal IT support. D2D2T solutions combine the reliability of tape and the speed of disk with network connectivity and qualified software in an easy-to-implement package.

"Recovery speed, combined with disaster recovery capabilities, is the ultimate benefit of a D2D2T solution and the underlying factors in any business's choice of a data protection solution. Not only is there a need for affordable equipment and cost savings by budget-conscious businesses and time-strapped IT departments, but there is also a need to protect the inherent value of corporate data. The needs to ensure complete and reliable backups, to quickly restore data in the event of loss or disaster, and to satisfy ever-increasing compliance requirements have never been greater."

He believes that D2D2T solutions offer businesses a far superior way to protect and manage their mission-critical information than tape or disk alone by delivering an impressive array of features at an affordable price point, "ensuring that SMBs don't have to choose between saving their data or saving their budget".

The debate raging over the respective merits of disk and tape is not going to end soon, of course, as Symantec's chief scientist Guy Bunker is only too aware. "Tape still has a future as compliance-influenced archival continues to spiral. Tape is also essential in any disaster recovery scenario as a last line of defence, and offers cheap and efficient answers to many questions.

"However, the requirement to use tape is diminishing as disk costs fall, as in the case of SATA drives for example, and capacities increase," he adds. "Backup is not actually about backup any longer, rather it is all about the restore - how quickly do you need your data back? If information is absolutely critical to your business, then the increased reliability of disk is a significant differentiator. Also, the random access nature of disk (as compared to the serial nature of tape) makes it much more efficient, and new software technology means that backups can become more intelligent because restore no longer has to be streamed off a tape.”

Bunker is at pains to point out, however, that while disk may seem the way forwards, there needs to be management around it. When a disk fills up, something needs to be deleted or else the backup will fail - unlike tape, where an old tape is removed and managed completely offline and a new tape added.

"If there are concerns over how much data needs to be backed up and the growth of online storage, moving to disk-based backup is just going to aggravate the problem - but the benefits outweigh the problems, as long as the correct architecture is created in the first place. So the real question is: what and why are you backing up? If this is mission-critical data, then there are new technologies which can create a backup in a few seconds, and then move the actual processing and data transfer to a secondary server: technologies such as snapshots, local and wide area replication, continuous data protection and clustering. If you are backing up as a last defence for disaster recovery, then you can still use these methods, but tape is still the most cost-effective medium to store data in the long term."

Bunker believes that businesses should be looking to an holistic strategy for backup - prioritising their disk data while ensuring that other methods are considered in relation to circumstance, budget and the business value of that data. "With the advances in solid-state memory, it will be disk which will disappear long before tape does," he concludes.

The current wave of disk-to-disk-to-tape (D2D2T), traditionally a mainframe feature, really exploded for open systems market with the deployment of SATA-based drives as a low cost alternative to higher cost Fibre Channel devices.

"Initially hailed as 'the end of tape', in truth this medium has merely stimulated repositioning of the reel-based technology for archiving and point-in-time backups for period-ends/snapshots before system down times," states Rick Terry, Viglen Storage Group - general manager.

He points to tiered storage - multiple layers of disk ultimately supported by tape or optical - as now moving from D2D2T to D2D2D…2T, with any number of intermediate disk layers based on capacity, performance, cost and reliability. Allied to this has been the recent evolution of high-power compression solutions to maximise the utilisation of the target medium, whatever that may be.

"Just as the introduction of low-cost tape autoloaders in the late 1990s revolutionised behaviour in departmental and remote backup regimes at that time - a change that continues to ripple down the business pyramid to the SOHO market - so, too, will the inclusion of disk as a backup medium and eventually even the concept of virtualisation.

"Disruptive to this technology trickle-down, of course, as always, is the Internet," he comments. "Vaulting services for end users, either from third parties or provided by in-house IS departments (utilising a virtual private network or dedicated point-to-point connection) have grown dramatically in recent years, following the availability of block-level backup software packages and growth in available bandwidth.

"Such services have mostly been built on D2D2T architectures, but mask this complexity from end users by means of a service-based offering with serious advantages, such as 'instant off-site' backups, which can form an important component in the disaster recovery/business continuity armoury."

So, ultimately, which medium is best for backup? "Selection should not be based on a bias for either disk or tape, but on the design of the backup architecture and performance requirement. Disregard either at your peril. As always, it is best to seek professional advice from a storage specialist such as Viglen Storage Group for an independent, but informed, view of the best solution to a given environment.

According to Gerard Marlow, disk business development manager, Hammer, a 'winner takes all' argument has continued over the past two years and more between the proponents of disk-to-disk (D2D) and disk-to-tape (D2T) as to which offers the better storage solution.

"Those favouring D2D have pointed to the superior performance and capacity of disk, just as supporters of D2T have emphasised the latter's long-term archival capability and its portability, supporting disaster recovery strategies through the ability to remove data off-site.

"However, over the past twelve months, the emergence of disk-to-disk-to-tape (D2D2T) has created a third option, one in which D2D and D2T can co-exist in the same solution. This has enabled a more mature debate, replacing a confrontational 'either/or' outcome with a purchasing decision more closely aligned to the broader needs of the business."

And this is an important step forward, for the arguments of both protagonists are valid. "For many businesses, there will be a requirement for fast back-up and restore for those parts of their data which may need to be accessed on a daily basis," adds Marlow. "At the same time, increasing demands for regulatory compliance - as well as good business practice - will demand that other information within the business will need to be stored and held over an extended period."
There are, however, cost implications. At this early stage of its development, D2D2T is more expensive and has been considered as an essentially enterprise-scale solution, though as capacity points come down, so entry-level solutions are already - if slowly - coming within reach of medium business users.

"In deciding whether a more costly D2D2T solution will in fact be the most cost effective, the SME will also need to take into account a number of broader business issues. For an organisation with limited bandwidth, for example, D2D2T will significantly reduce the strain on the network and improve performance of the company's overall IT infrastructure.

"Similarly, if back-up is an existing problem, the greater speed of D2D2T reduces the back-up window, so minimising scheduling problems and their impact on the daily running of the business. And finally, with its ability to specify archival life, the allocation of specific file types to disk or tape storage and better back-up data management, D2D2T is ideally geared to support those businesses looking to adopt Information Lifecycle Management (ILM) practices.

In the world of backup therefore, it seems you can have your cake and eat it." ST