Lakeview Says XSM Shows Promise As Young Technology for HA

by Alex Woodie

The latest release of OS/400 contains a new high availability capability called Cross Site Mirroring (XSM), which gives iSeries shops an entirely new way to replicate data to off-site backup machines. XSM allows you to mirror one independent Auxiliary Storage Pool to another on a remote machine. Lakeview Technology is supporting XSM with its own OS/400 mirroring software, called MIMIX, and says XSM shows promise as a technology, just like remote journaling before it.

IBM has been enhancing its independent Auxiliary Storage Pool technology over the last several releases of OS/400. An iASP is useful because it allows a disk or a set of disks to be made available or taken offline while an OS/400 server is still running, without requiring an IPL. The advent of XSM is the latest iASP-related enhancement, but probably not the last.

When iASPs debuted, the capability to connect processors with a set of disks, on the fly, proved useful in server consolidation environments, where a given server is asked to process a variety of workloads. It has proven a valuable virtualization technology, and has the advantage over logical partitioning in that it doesn't require the user to buy another OS/400 license. With OS/400 V5R1 and V5R2, IBM further refined iASPs with switched disk capabilities, or switchable iASPs, which allowed more than one system to access the same disk or set of disks (but only one system at a time, please!). Switchable iASPs were nice for planned downtime, when data needs to be kept available while one system is taken down for maintenance.

With XSM, IBM has taken iASPs to the next level. Once a switchable iASP has been set up, XSM will mirror that iASP to backup system and keep it up-to-date without any changes (and with a minimum of fuss from operators, we're told). In the event of an outage or planned downtime, XSM replication can be turned off, and then the backup system becomes the primary system, and vice versa. As with switchable iASPs, no two systems can ever access the same iASP at the same time. For the record, XSM works at the page level and uses operating system resources, and, as a form of hardware clustering, requires OS/400 Option 41 to be activated.

There are several things that XSM is good at, says Paula Stewart, Lakeview Technology's director of product strategy. It can replicate database files, data areas, and data queues. "Once you get the whole configured and implemented, you don't have to do a lot of babysitting," she says. "If your COM line is set up, you can feel good that IBM is taking good care of your data."

In some cases, XSM could be used in lieu of periodic tape backups. In that case, because it's constantly mirroring data and changes, XSM could provide a very good recovery point objective, which is a measure that high availability providers use to describe how far back in time you can expect to recover your data if there's a crash. "In our case, we can provide that as well," with MIMIX, Stewart says.

Lakeview has delivered support for XSM into the most current release of MIMIX V4R4, which the company recently rebranded as MIMIX ha1 (along with OmniReplicator, which is now MIMIX replicate1). Lakeview delivered XSM support in MIMIX ha1 as a service pack, which officials say has become the company's preferred method of delivering both fixes and enhancements these days. Because only one application can access an iASP at a time, changes needed to be made in MIMIX to ensure that applications were looking at the right copy of the data, Stewart says.

While it may sound like XSM could be used as a replacement to a product like MIMIX or any of the other high availability products that mirror OS/400 files and objects, there are a few little "gotchas" with XSM that users should consider before taking the plunge, says Glenn VanBenschoten, Lakeview's vice president of product strategy. One is that XSM doesn't replicate things like user profiles, authorization lists, or configuration objects. While it may be possible to get a backup site up and running without these items, it could be difficult to do so without compromising security. "What IBM has provided is a technology enabler, not a complete solution," VanBenschoten says.

Another drawback of XSM in its debut is that it does not replicate files that use constraints or commitment controls, which seriously limits its use in production environments. "If you're starting from scratch, and you didn't have data or a set of applications already written," XSM could be useful, VanBenschoten says. "The problem is getting there from where you are today."

XSM in its first release reminds Stewart of another promising young technology from IBM that took some time before finding its place in the industry. "That's was what was said when remote journaling came out. Remote journaling is a technology, a very fine technology, and a transport mechanism. Lakeview views itself as an information availability provider, and that includes providing the service, support, and training--providing the overall solution. Remote journaling has become a very important piece of that, and so will XSM," she says.

Remote journaling, of course, provided the low-level technological "plumbing" that allowed two newcomers, iTera and Maximum Availability, into a market that had been dominated by Lakeview, DataMirror and Vision Solutions, each of whom paid lip service to remote journaling but rarely sold it. The success of lower cost, remote-journaling-based high availability solutions prompted the established vendors to develop their own, such as MIMIX ha Lite, which Lakeview launched in March.

It will be interesting to see whether cross-site mirroring follows in remote journaling's footsteps and spawns a new class of availability solution for the iSeries. "It's a young technology," Stewart says of XSM. "It needs to mature, and as it does mature, it will get more interesting."