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The sheer volume of corporate data is skyrocketing, often resulting in unacceptably long backup and restore windows. Plus, the value of data is also increasing as more work is performed electronically, and the financial/legal penalties for lost data just get more and more severe. These days, storage administrators are looking for alternatives to tape to meet their business' growing demands. "I think I've backed up something [to tape] and I want to restore it, but there's a 30% probability that it will fail," says Arun Taneja, founder and consulting analyst at the Taneja Group. "Something like that would never fly in many parts of IT, but for data protection it's been the best we could do."
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Understanding D2D tradeoffs
The appeal of disk as a secondary storage target is easy to understand. Using disk can accelerate backups (reducing the backup window) and restoration, which can enhance the service levels for important data types in the organization. Disks are also more reliable than tape, improving the reliability of backup and recovery processes. Maintaining a local copy of data on disk also reduces the time wasted locating or shipping tapes. "Our research shows that the need to improve business continuity and disaster recovery operations, and the need to reduce tape library operational expenditures are also key business drivers that are fueling D2D adoption," says Heidi Biggar, analyst at the Enterprise Strategy Group.
But compliance issues have also played a role in the emergence of disk-to-disk. Government regulations and corporate governance concerns are forcing organizations to retain increasing amounts of data for longer periods of time -- which vastly increases data volumes. And, that data must be accessible to regulators in much less time than would otherwise be needed to restore and search huge tape collections.
Virtually every large IT department implements some form of disk-based protection, but analysts point out that overall disk-to-disk deployment is still in its infancy. "In the global 2000, the prevalence of disk right now is only between 5% to 10%," Taneja says. Even the most progressive corporations are only protecting about 10% to15% of their applications with disk-to-disk products, with most noncritical applications still relying on tape backup. Even though the added performance and reliability of disk-to-disk may not be necessary for every application, Taneja says there is still enormous potential for deployment.
In spite of the compelling benefits offered by disk technology, there are some important disadvantages that must be carefully evaluated before any purchasing decision is made. The biggest problem is the up-front expense. "Seventy-four percent of respondents to our survey (March 2005) said acquisition cost was the greatest impediment to their organization implementing these types of solutions," Biggar says.
Management requirements pose another concern. The inclusion of another storage tier means there is more equipment to manage and more storage space to prepare, provision and maintain. Additional tasks can potentially place a strain on limited IT resources. "It's extra work for them," Taneja says. "But I happen to think that the net benefit [of disk-to-disk] is huge."
Finally, disk media cannot be transported off site, and this can present a significant issue for companies that traditionally rely on tape for off site data protection. As disk-to-disk systems appear, existing tape systems are being pressed into service in a tertiary role, often backing up the secondary disk contents for long-term storage or archiving tasks (e.g., a disk-to-disk-to-tape architecture). For example, a primary VTL may reside in New York City where it is replicated to a second VTL in Boston. The replicated VTL contents can then be backed up to local tape without impacting availability of the primary VTL or the production network. Tape media can then be shipped off site, if necessary.
Software differentiates D2D platforms
A disk-to-disk platform like CDP, VTL or CAS requires both hardware and software. Analysts are quick to note that the emergence of low-cost, high-performance SATA disks has really enabled disk-to-disk technology -- the disk-to-disk platforms that we see today simply would not have been economically feasible without cost-effective disk media. When you eliminate the fancy acronym, however, each disk-to-disk system is basically a disk array. The software element is what really differentiates one disk-to-disk system from another. "SATA hardware is at the heart of this," Taneja says. "But outside of that is all software."
Vendors and product selection
The disk-to-disk area is so broad that it's difficult to identify every potential vendor in this space, but it's possible to classify the most notable vendors in several key aspects of the technology. Disk-to-disk software vendors (in no particular order) include Computer Associates Inc., CommVault Inc., EMC Corp. (Legato), Symantec Corp. (Veritas) and Atempto. Generic disk-to-disk "disk-as-target" vendors include Advanced Digital Information Corp. (ADIC), Nexsan Technologies, Network Appliance Inc., Asigra Inc., Avamar Technologies Inc., Signiant Inc., and Hitachi Data Systems,Inc.. VTL-specific disk-to-disk providers include EMC, FalconStor Software, Hewlett-Packard Co. (HP), Sepaton Inc., Diligent Technologies Corp., Network Appliance Inc. (Alacritus), Neartek Inc., Quantum Corp., Data Domain Inc. and Overland Storage. Many of the most notable disk-to-disk product vendors are represented in Diogenes' Lab Test Flame Ratings chart.
One of the most notable features to appear in disk-to-disk product discussions is data deduplication, which appears in the DD 400 system from Data Domain and others. "Diligent has recently released their 'HyperFactor' product, which conceptually does the same thing," says Phil Goodwin, president of Diogenes Analytical Laboratories Inc. "However, there's still a lot of differentiation between methods once you look under the covers."
Goodwin's recent disk-to-disk product evaluations [see the sidebar on this page] also cited ease of use and functionality as key aspects of product selection, with most products such as HP's VLS6500 offering excellent installation and support, as well as very good interoperability. "That [HP] product is so simple that an eighth grader could install it," Goodwin says. "We were able to install it and get it working in less than an hour."
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