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Most enterprises understand that the only way to ensure data protection and IT continuity in the face of disasters is to establish a remote recovery site a significant distance from main and branch offices. As a result, every night many companies back up their office systems to tape and transport the tapes anywhere from fifty to several hundred miles away. What these organisations haven’t recognised is just how vulnerable their data and business remain, even after such a huge outlay of administrative effort and cost.

What’s wrong with Tape Backup?

Many of the problems with tape backup are well known; tape hardware, media and software are expensive and even after the investment of time and money has been made, recovery is by no means certain to be successful. However, there are other issues, implicit in the use of tape, which are fundamental to the success or otherwise of attaining business continuity goals that need to be understood.

Tape backup places limits on an organisation’s Recovery Point Objective (RPO), the past point in time to which you can recover data after a disaster. Suppose, for example, that a critical system fails sometime today; the best you can do is recover to yesterday’s data, which will be at least twelve hours old. The later in the working day disaster strikes, the older the data from which you’ll recover. The cost of permanently lost data is high and includes the cost of the revenue that the data represents, the business value you can extract from it, and the cost to recreate it.

The key to a successful disaster recovery plan is to focus not just on the data (RPO) but also on the applications that end users run to gain access to that data.  The Recovery Time Objective (RTO) is generally defined as the amount of time it takes to regain access to business-critical data. When a large-scale disaster strikes, with tape backup a company is out of business until it can restore systems and data from its tapes. This kind of restoration takes a minimum of several hours, and can easily take days or even weeks. Tape backup does not provide the level of recoverability that most enterprises require.

Another considerations, is that the process of making a tape backup takes place during a ‘backup window’, during which systems being backed up cannot be used. Given the ever-increasing demand for around the clock data access, it has become much harder for companies to complete nightly backups within the time provided.  In many cases, once-nightly backup goals slip to every other night for some machines. At remote branch offices, where the process is often left to non-IT staff, backups may be less frequent still.

Many enterprises that rely on tape backups have not properly considered the following questions: How much would it cost your organisation if all of your transaction data for the last twelve hours were lost? What is the value of the knowledge contained in your company’s last twelve hours worth of e-mails and e-mail attachments? What is your exposure if you can’t produce this data in compliance with your industry’s regulations?

A Better Solution: Continuous Data Replication
Data replication provides a continuously updated copy of critical data at a remote site. In the event of a disaster, users are rapidly failed over to the live backup systems at the remote site, minimising data loss and greatly speeding recovery. Disk-based recovery is more reliable, less complex and takes less time than tape-based backup, improving the RPO and RTO of the disaster recovery solution.

Data replication has long been considered an impractical solution for data protection and recovery, especially for small or medium-sized business with limited resources.  Historically, it required expensive hardware and a large investment in bandwidth to replicate and protect data in real-time. However, the recent evolution of replication solutions is starting to dispel this belief.

Within software-based data replication, there are two major technologies: synchronous and asynchronous replication.  It’s important to understand the benefits and drawbacks of each.

With synchronous replication, the software intercepts data being written to disk and sends it to both the primary and secondary disk arrays at the same time. Only when both arrays confirm receipt of the data does the software accept another write. With synchronous replication, data loss approaches zero because both the primary and secondary disk arrays must contain the same data. However, the confirmation process can cause performance problems, especially in applications that process lots of transactions.

Acceptable performance of synchronous solutions often requires connecting the arrays with high-bandwidth fibre channel, which is very expensive and has an effective range of about ten miles. As a result, synchronous replication is most often used to create a local backup of data in situations where having an exact copy of the data is essential.

With asynchronous replication, the replication software grabs data once it is written to disk, and rewrites it to a second array. The application doesn’t have to wait for confirmation so it can operate with little or no impact on application performance. It can also use low a bandwidth connection over any distance. Asynchronous replication provides enterprises with a very high degree of data protection and makes the most cost-effective use of existing infrastructure.

While asynchronous replication can’t deliver the zero data loss available through synchronous replication, it can be configured to deliver RPOs and RTOs that are more than acceptable for most business uses. The combination of excellent data protection, minimal performance impact, long-distance effectiveness and low-cost deployment makes asynchronous replication an ideal solution for backing up data to a remote recovery site.

Conclusion
There was a time when tape-based backup was widely believed to be the only feasible backup solution for remote offices. However, relying on tape backup is expensive, complex and cause a company to incur additional expenses related to recreating lost data. In the worse case, relying on tape backup can significantly impact the ability of a business to continue trading after a disaster.

Advances in technology have made centralised backup through data replication easier to manage, taking the responsibility for backups out of the hands of non-technical resources in remote offices, and giving it to the experts back at a central data centre. Replicating data to a central location from branch offices can reduce the per-location costs associated with tape-only solutions and provide a higher level of recoverability for business-critical systems and data.

Augmenting or even replacing a tape-centric data protection scheme with continuous data replication, can have a significant positive impact on protection budgets at the same time as providing a far higher level of protection and recoverability than tape.

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