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Sometimes VMware Virtual SAN (VSAN) performance doesn't live up to expectations. This usually occurs because a...
VSAN is designed to act as shared storage for an entire host cluster. You won't see a performance gain if you use a VSAN to host a single virtual machine (VM). If you need to host a small number of VMs, you can set the striping policy to a higher number. However, this technique is only effective as long as the cluster isn't overly busy.
VSANs have also been known to behave erratically or unreliably. In many cases, this is due to driver or firmware problems. While VMware maintains a hardware compatibility list for its products, deviating from this list may sometimes yield satisfactory results -- or just the opposite. There is no guarantee of proper VSAN performance if you use an unsupported hardware configuration. Keep in mind that VMware's compatibility list addresses hardware components as well as drivers and firmware.
But even if you adhere to VMware's hardware compatibility list, it is possible to end up with VSAN performance issues due to inadequate hardware. For example, VMware cites the example of a VMware administrator who doesn't understand the performance implications of using a single 4 TB 7,200 rpm drive as opposed to four 1 TB 10,000 rpm drives. The vendor also notes that some users receive poor performance because they try to cut corners by using low-end components with VSAN.
According to VMware, most users are better off using pre-configured VSAN ReadyNodes. The vendor has an available design and sizing guide that explains the various technical concepts behind selecting appropriate hardware for a VSAN.
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