Humans are tool makers. The fact that we can make and use complex tools (including tools that help make other tools) is part of the reason for our evolutionary success as a species. Tools such as the axe, the saw, the steam engine, and the microprocessor have dramatically changed human society. Over the years, we've created many tools to save labor or time by simplifying complex, difficult, or dangerous tasks.
In the IT world, we have a lot of tools, many of which are intended as laborsaving or timesaving devices, and some of which actually live up to that promise. The latest wave of tools includes many products that vendors have packaged as standalone appliances, providing useful services with little or no administrator attention or intervention. These devices include spam and virus filters, SAN and network storage units, firewalls, and various special-purpose devices for network monitoring and control.
Some of these appliance classes have become popular in the marketplace. For example, spam-filtering appliances have gained noticeable market share on the basis of their ability to deliver services with less hassle than other ways of providing those same services. Each successful appliance spurs vendors to look for new applications that they can package as appliances, the latest being Exchange disaster recovery.
A company called Teneros now offers Exchange disaster recovery through a high availability appliance, the Teneros Application Continuity Appliance for Microsoft Exchange, that offers automated disaster recovery. This is certainly an appealing prospect, given that most of us don't practice disaster recovery as often as we should and that failures usually happen at inconvenient times. The question, of course, is what such appliances do and whether you can trust them to do it properly. I spent some time talking to Teneros representatives at the recent Exchange Connections show; here's how they explained their product.
The Teneros appliance contains what amounts to an embedded Exchange server, which is controlled and monitored by a second embedded computer running Linux. The Linux machine communicates with Teneros's service center to install firmware updates, patches, and the like, and to provide remote monitoring and control of the appliance. You plug a network cable from your Exchange server into the Teneros appliance, then plug the appliance into your network.
The appliance monitors the state of your production Exchange server and replicates all transactions to the backup unit inside the Teneros box. If a failure takes place, the Teneros unit impersonates the network address of the failed server, allowing effectively seamless failover. The demos are impressive; failover takes only a few seconds and is transparent to the client. The appliance stands in for your Exchange server and lets users work normally until you restore the production server and bring it back online, at which point normal operation can resume.
Teneros has an interesting pricing model. You buy an appliance that has the storage capacity needed to hold your Exchange data; the price includes the necessary Windows and Exchange licenses for the appliance. In that light, you should compare its pricing to the cost of an additional server. One problem with this model is that each Teneros appliance can handle only one Exchange server; if you have a lot of servers to protect, you'll end up with a lot of appliances.
A few things keep me from recommending Teneros's appliance unreservedly. The Teneros employees I spoke to were unclear on the exact replication method used. It's not Messaging API (MAPI), and it's not direct replication of Extensible Storage Engine (ESE) pages on disk, but they couldn't or wouldn't tell me exactly how transactions were captured. Without knowing that, it's hard to form an opinion of the fidelity of the replicated data. It's also not clear how much management access you have to the Exchange server embedded within the appliance. For example, if you apply a hotfix to your production server, can you apply it directly to the embedded server or do you have to wait for Teneros to apply it for you--and if so, is there an impact on supportability? I'm hoping to get some hands-on experience with one of these units over the summer; I'll report back on what I learn. In the interim, though, this appliance might be worth looking into as a way of simplifying your disaster-recovery plans.
A gentle reminder: The first day of June is the official start of the Atlantic hurricane season. If you're near the coast and don't have an up-to-date disaster-recovery plan, you should develop one posthaste. It's worth remembering that large storms can strike anywhere on the eastern coast of the United States and Canada--don't assume that they're only a Gulf Coast problem. Even if you're not in a hurricane-prone area, this is a good time of year to revisit your disaster-recovery and high availability strategies and to ensure that they reflect your business needs.