Scalable Storage Performance: VMware® ESX 3.5

VMware ESX enables multiple hosts to share the same physical storage reliably through its highly optimized storage stack and VMware Virtual Machine File System (VMFS). Centralized storage of virtual machines using VMFS provides more control and flexibility. It also enables such unique virtualization capabilities as live migration (VMware VMotion), VMware Distributed Resource Scheduler, VMware High Availability, and clustering. To gain the greatest advantage from shared storage, you must understand the storage performance limits of a given physical environment to ensure that you do not overcommit resources. To make the most effective use of your storage, you need to understand: How many virtual machines can share the same LUN How SCSI reservations affect shared storage performance in ESX How many LUNs and VMFS file systems can be configured on a single ESX host This paper presents the results of our studies on storage scalability in a virtual environment with many ESX hosts, many LUNs, or many of both. It examines the effects of I/O queuing at various layers in a virtual infrastructure as more and more virtual machines share the same storage. It considers the effects of SCSI reservations on virtual machine I/O performance. And it looks at ways to mitigate bandwidth bottlenecks when multiple LUNs are connected to a single ESX host. It provides recommendations you can follow to avoid overcommitting storage resources. This study covers the following topics: “Measures of Scalability” on page 1 “Factors Affecting Scalability of ESX Storage” on page 2 “Summary of Storage Scalability Recommendations” on page 9 “Conclusion” on page 10