Stratus Builds Its First HA Clustering Product Atop Xen

Published: June 17, 2008

by Timothy Prickett Morgan

The age of virtualized servers is going to have some intended side effects on the server racket, and one of them is high availability clustering that is easier to use, more flexible in its deployment, and less costly than more tradition server clustering methods. While Stratus Technologies is one of the original upstarts of fault tolerant computing (along with Tandem, now a division of Hewlett-Packard), the company knows a broader HA opportunity when it sees it. And that is what the Avance virtualization-driven HA software product line announced this week is all about.

To make its point about how easy it is to use, Stratus executives hosted a Webinar launching the product with the press last Tuesday and showed a video clip running during the announcement as two Dell PowerEdge servers were clustered together running Red Hat Enterprise Linux with a mere few clicks of a mouse. (The cluster was set up and running in under 30 minutes, the length of the Webinar.) The Avance HA application is a derivative of the ftServer fault tolerant hardware and microcode that Stratus has developed and then tweaked with partner NEC over the years. (Why NEC doesn't just buy Unisys and Stratus and make a bigger move in the North American market is a bit of a mystery. Or, HP for that matter. Both companies would be a good fit for HP, too. And Dell needs more help than NEC or HP in the server space. . . . )

With ftServer fault tolerant setups, Stratus takes servers from NEC and equips them with chipsets and firmware that allows for the absolute lockstepping of applications running on two distinct physical machines. These machines are identically configured, including identical processors, memory, disks and such, and they can provide 99.999 percent uptime, which is fabulous. That extra engineering, however, drives up the price of the ftServer, of course, particularly because it is a relatively low volume product; two-socket boxes range in price from $12,500 to $21,250 from Stratus, for instance, depending on the features installed. The machines from NEC support Windows or Linux workloads, and are based on dual-core and quad-core Xeon chips from Intel.

The problem with the Stratus and NEC fault tolerant boxes is that they tend to lag the latest processor and hardware technology because of the length of time it takes to tweak machines to use the ftServer secret sauce. Moreover, the product line is fairly limited, and if you happen to like servers from Dell, HP, IBM, Sun Microsystems, or Fujitsu-Siemens, well, too bad.

Enter Avance. Because the product is based on the XenServer hypervisor from Citrix Systems, by its very nature it deals with servers that are already being abstracted by the hypervisor. And that means that Stratus can bury its secret clustering sauce in that hypervisor layer, masking it from operating systems and applications. Unlike some HA clustering setups, which require shared SAN arrays for clustering, the Avance product does not require SAN storage, and it also does not require even identical storage configurations on the two servers to be clustered. In fact, the two servers do not have to be similar in any way except that they can run Windows or Linux, support XenServer, and have enough processor, memory, disk, and I/O capacity to support the workloads on the primary machine. They also need an Ethernet link between the two boxes to be clustered, which is used for data replication between the disk drives on the two machines to be clustered. (The software does not cluster two physical machines that are not using operating systems running on bare iron, by the way.)

Stratus is saying that it can deliver 99.99 percent availability--that's less than an hour of downtime a year--on virtual machine partitions running Microsoft Windows or Red Hat Enterprise Linux atop of the Avance HA software. The product includes a license to the XenServer hypervisor, and has support for 64-bit native guests operating systems (so long as they are Windows or RHEL, for now). The setup allows up to eight virtual processors inside of a virtual machine partition, which is plenty big enough for a lot of workloads. And not needing the machines to be identical or to have SAN attachment for storage is a big deal, too.

Rather than push Avance directly, as Stratus does with the ftServer line, it is taking a channel approach to pushing the product, particularly since it is being aimed at small and medium businesses that, until now, had tape backups or complex HA heartbeat and data replication tools as their option--as well as buying fault tolerant machines from Stratus, NEC, or HP. Dell is the first vendor to have Avance certified on its PowerEdge server line, and it is particularly interested in peddling the virtualization-driven HA solution to retail and healthcare companies that need HA but can cope with complexity or pay high prices. While Dell is providing the front line tech support for Avance, Allan Jennings, senior vice president of product and solutions development at Stratus, says that companies who want Stratus to support their Dell-based clusters can buy an optional support contract.

It also seems likely that other server makers will step up and sell the Avance software, or come up with their own. And while VMware's ESX Server hypervisor is the default hypervisor of choice in data centers today, the closed source nature of the code and the company's own aspirations in the HA area make it hard to support ESX Server and relatively easy to support XenServer. (ESX Server is the hypervisor of choice on the ftServer line, so Stratus knows what it is talking about here.) The Avance HA product only spans two-node clusters today, but Stratus hinted that the product was designed to handle larger numbers of nodes and more sophisticated HA setups. (It would be nice, for instance, to have clustered machines onsite and a hot backup in a geographically distant data center.)

Avance costs $2,500 per server node, and companies obviously have to buy two nodes to make an HA cluster. This price includes a license to XenServer Standard Edition, which costs $780 per server for a perpetual license if you buy it directly from Citrix, plus a $120 annual support contract. Customers acquiring Avance have to pay a year's maintenance on the software as well, but pricing was not available at press time for support.

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