Review: VMware VSAN turns storage inside-out


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To compare my two clusters, I ran two different I/O Analyzer workloads to measure high write performance and a mixture of reads and writes. The Max IOPS test used a 512KB block size for 100 percent sequential read, while the combo test used 4KB blocks and a mix of 70 percent reads and 30 percent writes. The results of the two tests tell two different stories. Whereas the three-node cluster held its own against the four-node cluster in the Max IOPS test (roughly 154K vs. 190K maximum total IOPS), the four-node cluster proved vastly superior (yielding roughly double the performance) in the mixed workload test. The results of the mixed workload test are presented in the chart below. 

With more RAM, more CPU, larger SSD, and 10GbE networking, the three-node Supermicro cluster more than doubled the read and write performance of the three-node Lenovo cluster.

The single most important factor in VSAN performance will be the size of the SSD cache. If the data your workload requires is not found in the flash cache, but must be accessed from rotating disk, then I/O latency will shoot up and IOPS will fall dramatically.

Note that the results for the mixed workload test shown above make use of 4GB target virtual machine disks, which (when multiplied by eight I/O Analyzer workers per node) did not exceed the SSD cache size in either cluster (100GB SSD in the Lenovo nodes, 400GB SSD in the Supermicro nodes). When I ran the same benchmark using 15GB target disks for the Lenovo cluster and 50GB target disks for the Supermicro cluster (exceeding the SSD cache size on all cluster nodes) IOPS plummeted on both clusters.

In short, when configuring your VSAN cluster hardware, be absolutely sure to include enough flash in each node to exceed the size of the working data set. Naturally, more RAM and 10GbE networking are nice to have. VMware recommends 10GbE for most deployment scenarios. After all, the cost has dropped considerably over the last few years, and 10GbE offers significant improvements in performance over 1GbE.

Think global, store localVMware's Virtual SAN represents a significant step toward the stated goal of a software-defined data center. It's also somewhat of a "back to the future" experience, with storage moving into the local host machines and away from a centralized and dedicated storage appliance. My testing shows that VSAN is capable of delivering respectable performance on moderately priced hardware. Throw in 10GbE networking and you'll see impressive results on even the lowest-end hardware configuration.

Once you get past the initial disk configuration, the installation process is no different than any other VMware setup. Configuring and managing VSAN should be relatively painless for most customers. That said, VSAN is a 1.0 release: Those who need to tweak the settings may have to do some digging, reading, and testing to get what they want. The vCenter tools and the VSAN Observer offer deep insight into what's happening inside the kernel to help diagnose any significant issues. VSAN supports up to 32 nodes and 35 disks per node. If you do the math, you'll find that scales out to a whopping 4.4 petabytes of storage with current disk technology.

Published costs for VSAN start at $2,495 per CPU, which translates into roughly $20,000 for the high-end Supermicro cluster. For the Lenovo cluster, the price of VSAN would be $14,970 or roughly twice the price of the hardware. VMware also sells VSAN at a price of $50 per concurrent or named user for the aforementioned VDI scenario. That makes much more economic sense for smaller deployments. It also makes sense when you get into the higher-end configurations and begin to compare the price of VSAN with that of a traditional storage system from companies like VMware's parent EMC.

The final verdict comes down to economics and implementation. VSAN in the current release has a tightly focused target use case in VDI, where it offers compelling advantages in initial cost and long-term maintenance and support. The use cases for VSAN will undoubtedly broaden over time, but that's not a bad start for a version 1.0.

This article, "Review: VMware VSAN turns storage inside-out," was originally published at Follow the latest developments in virtualization, data center, storage, and cloud computing at For the latest business technology news, follow on Twitter.

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