Remote Journaling: Friend or Foe in HA?
Published: February 8, 2011
by Alex Woodie
Is remote journaling a benefit or a hindrance in IBM i high availability solutions? Since it debuted in OS/400 more than 10 years ago, HA software makers have touted remote journaling as a technological godsend, claiming it simplifies the development of HA solutions, and streamlines its operation. However, not all HA software developers are singing that tune any more, and at least one is saying that the fact that its HA solution is not based on remote journaling gives it a technological advantage.
For those who have been watching the soap opera that is the IBM i HA software market, this statement--that remote journaling is bad, or at least not as good as the alternatives--is a deliciously ironic twist. For many years, upstart vendors like iTera and Maxava touted the superiority of remote journaling over older, proprietary replication methods that were in widespread use with Vision Solutions, Lakeview, and Datamirror (since gobbled up by IBM). Since remote journaling was built into the operating system layer (actually, below the OS layer, but let's not get into that!), it simplified the development of HA products, streamlined the management of the HA processes themselves, and minimized processing hits on the production machine. Or so they said.
Now, the companies that develop and sell the Quick-EDD HA software, including the French company Trader's and its master distributor in North America, iSamBlue, are touting the avoidance of remote journaling as a product differentiator.
iSam Blue CEO Robert Seal, who was one of the leading developers of the iTera's remote journaling based product, called Echo2 (which is now owned and sold by Vision Solutions), laid out the argument against remote journaling in a paper titled "No Latency: Why Quick-EDD/HA is What's Next for IBM Power i High Availability."
In the paper, Seal makes the case that Quick-EDD has lower latency, consumes fewer resources, compresses data better, and is straight-out faster than competing IBM i HA products. But it's the alleged latency--the time lag between when transactions are posted to the production machine and when they appear on the backup machine--that Seal claims is a major differentiator with Quick-EDD.
Seal claims that remote journaling has no way to ensure that journal entries are applied in the proper sequence on the target machine. In the event of an unexpected outage, Seal says this may require a user to apply hundreds of thousands of journal entries before the target system is as up-to-date as the production machine before it went down.
"Users must find the missing transactions, then enter them without updating information already replicated. Or, they can just skip them and hope that nobody notices," he writes in the paper. "Now you know why other HA vendors either do not talk about the latency issue, or minimize its impact."
While Trader's may be a new name to North American IBM i shops, it's no spring chicken in this business. The Paris-based company has been developing its Quick-EDD software for nearly 20 years, and claims over 1,000 installations, most of which are in Europe. Seal says that, after comparing remote journaling to its own proprietary communications protocol, Trader's developers decided not to convert to remote journaling, as most of the vendors in North America did.
HA Vendors Respond
The IBM i HA market is no stranger to controversy. In fact, the subject of remote journaling has been a major issue in this market before.
From about 2001 until Vision's parent company bought iTera in 2006, iTera transformed the North American IBM i HA market, largely on the basis of its claims that its brand of remote journaling-based HA was cheaper to buy, easier to install, and simpler to maintain. New Zealand-based Maxava has also made its reliance on remote journaling a major part of its overall business strategy. More recently, other IBM i software vendors have jumped into the market with remote journaling-based HA solutions, including Bug Busters Software Engineering with its RSF-HA, and Shield Advanced Solutions with its HA4i.
One big supporter of remote journaling is Vision Solutions, which acquired its competitors iTera and Lakeview, and is by far the biggest IBM i HA software vendor in the world.
"Over the last decade, remote journaling has become the best-practice approach for virtually all the HA solutions in the market," a Vision spokesperson says. "IBM endorses it as the best approach as well. We have thousands of customers, both big and small, that span virtually every industry that are successfully using remote journal-based solutions." While most of its products are based on remote journaling, it still offers products that use "local journal-based mirroring" as well, Vision adds.
Simon O'Sullivan, a senior vice president with Maxava, is a fervent supporter of remote journaling as the basis for *noMAX. We drank the RJ Kool-Aid and it tastes great!" O'Sullivan tells IT Jungle. "Remote journaling is just fantastic, very efficient and getting better all the time in our opinion. We very rarely have any issues with it at all and our customers love it."
O'Sullivan questions the claim that remote journaling contributes to high latency. "There are many good reasons why it's the best way to get transactions from one machine to another, but one of the top ones is that things happen in real-time, and that is key with replication for HA/DR," he says. "It also uses very few system resources on the primary machine."
Each vendor is free to make claims about their products. Indeed, it's the very differences between similar products that make a software market vibrant and competitive and healthy. Unfortunately, it can be very difficult to confirm claims in the real world, which can lead to customer confusion. Perhaps it's finally time to put the leading IBM i HA software products to a real-world test, which would establish some kind of benchmark for performance.
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