Implementing an IP SAN for disaster recovery: using iSCSI as an enabler

Computer Technology Review, April, 2004 by Brian Irwin

Staying competitive in today's business environment requires constant access to up-to-date information. Highly-available access to customer and competitor data, financial documents, online transaction processing and ecommerce applications are essential to ensuring efficient and timely business decisions. In the event of a disaster, natural or otherwise, loss of access to critical data can be disastrous to a company.

Having a thorough, and tested, disaster recovery plan in place can be an immense help if a disaster were to strike. A good disaster recovery plan covers many more areas than just data access. However, for the purpose of this article, only access to information and business-critical data will be considered. By implementing a Storage Area Network (SAN), an organization is able to ensure data high availability and redundancy. Further, IP SAN architectures based on the iSCSI protocol offer affordable solutions to the small and medium-size business (SMB).

Disaster Recovery Challenges

To any business, the major consideration to recovering from a disaster is one of cost. One major factor determining the amount of cost incurred is the time to recover. The longer the recovery time, the larger the revenue loss and the more difficult to financially overcome.

During the disaster recovery process, how will business be conducted? Are there processes or plans in place to allow you to continue business until your systems can be recovered? Will you have application and data availability during this period? These questions and others should all be considered, answered, and assumptions tested prior to a disaster. The primary recovery strategy for most organizations continues to be tape backup, especially in the SMB market segment. There are several shortcomings to this approach.

Implementing a LAN-based tape backup requires streaming data across the LAN to a backup server. During the backup process the LAN experiences significant performance degradation. To circumvent this problem, many companies perform their data backups overnight. The burgeoning amount of data needing to be stored is in direct conflict with the need for decreasing backup windows created by 24X7 business transactions.

Another shortcoming of tape is the media itself. Using tape repeatedly will cause the media to stretch. There is also direct tape contact with the head mechanism, increasing the chance of media contamination.

Finally, the largest downfall of tape is not the time it takes to back up, it's the time it takes to recover from a disaster or an equipment failure. Restoring from tape can take several hours to several days depending on the amount of data to be restored and whether full or incremental backups have been performed. This downtime is simply not acceptable to businesses wanting to stay competitive in today's data-driven business environment.

Despite the drawbacks stated above, tape is still a widely accepted storage medium. Tape archival can be an effective method of long-term data storage. However, if you are using tape as your primary disaster recovery method and you cannot tolerate a large restore window, it would behoove you to rethink your strategy. Current SAN technologies could improve your recovery scenario and help consolidate your storage infrastructure simultaneously.

Introducing iSCSI Storage Networking

Since the approval of the protocol, iSCSI has been steadily gaining acceptance among end users and storage vendors and is proving to be a disruptive technology. More vendors are now offering iSCSI products ranging from interface cards to routers, gateways, and storage devices. Initially there was much debate and skepticism about the speed of block data access over a network. The ability of host systems to process incoming and outgoing IP packets was a subject of major concern and endless debate. With the introduction of TCP Offload Engine (TOE) bus adapters, this concern has been lessened. The removal of the transmission processing from the host operating system and CPU to the HBA is paramount to providing improved performance on the host system and a big step toward iSCSI acceptance.

The Promontory Project has proven that, indeed, native wire-speed IP storage is possible. What this means is that IP storage networking is now viable for the SMB market segment. Fibre channel SAN infrastructures will not become obsolete any time soon--large organizations are very heavily invested in the technology. However, iSCSI offers the SMB segment the benefits of networked data storage without breaking the bank on more costly Fibre Channel solutions. Today, 100MB/s transfer rates are achievable with gigabit Ethernet. This aggregate throughput will increase with the introduction of 10, 40 and even 100Gbps Ethernet technologies.

There are other benefits of iSCSI storage to be realized by end users. First, Ethernet has a very large advantage by being a thoroughly entrenched networking technology. As such, most technical personnel understand the technology, which eliminates the expensive training needed to implement and maintain a large Fibre Channel solution. Another advantage of personnel being familiar with Ethernet is the ability to get their arms around an Ethernet-based SAN quickly. The learning curve is much shorter.