The Sun BluePrints article LDoms I/O Best Practices - Storage Availability with Logical Domains by Peter A. Wilson discusses the approaches and trade-offs for configuring highly available paths from Sun Logical Domains (LDoms) guest domains to storage.

LDoms is a virtualization technology supported on Sun core multithreaded (CMT) servers, which are powered by UltraSPARC T1, T2, and T2 Plus processors. LDoms allow server resources to be partitioned and allocated to separate virtual machines. This approach uses static partitioning that guarantees resources to guest domains, in contrast to typical hypervisors that timeshare resources across a set of virtual machines. In LDoms, resources can be dedicated down to the level of CPU thread, cryptographic processor, memory, and PCI bus.

Wilson explains more about LDoms architecture and its support of I/O domains, along with the features and benefits gained in an LDoms/Solaris OS environment. The following topics are covered:

“I/O Availability Overview”

Provides an overview of using multiple paths to the network to increase availability, and which solutions are available on which Sun servers.

“Multipath I/O with Solaris OS MPxIO”

Illustrates how to use Solaris Multipath I/O within a single I/O domain. Multipath I/O, whether implemented with MPxIO or IPMP, protects against any failure that makes all but one path in the multipath group unavailable. The combination of both technologies protects against both I/O domain and network path failures.

“Multipath I/O with Virtual I/O Failover”

Notes the benefits of virtual I/O failover to a multipath I/O configuration. Virtual I/O failover protects against the failure or shutdown of all but one I/O domain in the virtual I/O multipath group.

“Virtual I/O Failover and Network File Storage”

Discusses how IP multipathing can be used to provide highly available paths to network attached storage systems.

“Multipath I/O to Network File Storage with Virtual I/O Failover”

Discusses the benefits of combining IPMP with virtual I/O failover.

Conclusion

Overall, Wilson concludes that if availability were the only objective, combining both virtual I/O failover and multipath I/O would be the best approach. However, there is an increase in cost, and the total cost of the solution should be considered in the context of actual requirements.

"In many cases, for example, it would be acceptable to bring a guest domain down while a single I/O domain supporting it is patched or upgraded. With today’s application architectures built with the resilience to withstand the failure of one or more servers, protecting against the more common cable failure or switch misconfiguration may provide the most cost-effective solution," he writes. In the end, Wilson summarizes that both virtual I/O failover and multipath I/O provide effective tools for mapping best practices from the physical world into the virtual world provided by LDoms.

More Information

LDoms Product Page

Logical Domains (LDoms) 1.3 Released [...read more...]

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