Review: VMware Virtual SAN turns storage inside-out

Managing VSAN
The vSphere Web Client has seen many improvements since its introduction. For vSphere 5.5, you must use the new Web client for the large majority of management functions, including VSAN administration. The old Windows-based client is still there, but you won't be able to do much with it beyond basic VM management. You can still launch a remote console to any VM, which seems to work better and more consistently than the same process from the Web client.

I found the latest rendition of the vSphere Web Client to be more than adequate for most management tasks. At the same time, I found differences between the old and the new that took some getting used to. For some operations, it takes more than a few mouse clicks to navigate through the user interface and get to the point where you can actually make changes. That said, I really like the detail presented by the monitor page (see Figure 1) for both hosts and individual VMs.

VMware provides tools specifically for peering into the overall performance of the various moving parts of VSAN. For example, VSAN Observer provides a Web-based dashboard that shows latency, IOPS, bandwidth, and health statistics of the VSAN disks. Figure 2 shows the VSAN Observer dashboard with thumbnail graphs for each node in the VSAN cluster. Clicking on a "Full-size graphs" link opens up detailed graphs for each individual node.

VSAN supports VASA, the VMware APIs for Storage Awareness, allowing vCenter Server to report on a myriad of statistics and to implement storage policies (to ensure that storage requirements for virtual machines or virtual disks are met). Naturally, VSAN does not support VAAI, the VMware APIs for Array Integration, given there's no opportunity to offload storage operations from the host; you won't see a big performance boost for in-place cloning or reclaiming space with unmap. This is one area where a traditional SAN from EMC or NetApp would significantly outperform a VSAN solution. 

PowerCLI is VMware's PowerShell snap-in for driving vSphere from the command line. PowerShell is Microsoft's not-so-secret automation weapon, which means you'll need a Windows machine to actually run any scripts or use the command line. PowerCLI makes the repetition of commands much less painful and much less prone to error. I was able to use PowerCLI and PowerShell to automate much of the creating, modifying, starting, and stopping required to configure 32 virtual machines for all the performance testing described in the next section.

VSAN performance
One of my goals in testing VSAN was to compare the level of performance available on low-cost hardware (the Lenovo three-node cluster) against the higher-end (the Supermicro four-node cluster) and to attempt to identify hardware-specific issues that could be improved with an upgrade. I measured performance by using the VMware I/O Analyzer, a freely downloadable tool from VMware Labs that makes the process of measuring storage performance easier by combining a commonly available tool (Iometer) with nifty, Web-based control magic.

Version 1.6 of the VMware I/O Analyzer (IOA) consists of a 64-bit Suse Linux Enterprise Server 11 SP2 virtual machine with two attached virtual disks. The first disk contains the operating system and testing software, while the second disk serves as the target for the tests. All Iometer traffic targets the second disk in raw mode, so it will write to the device directly, bypassing any file system.