But nonetheless the other benefits caused this change to generally be recommended. This made it much easier to identify when something was configured wrong (not fully zoned etc).Ī third argument was performance, but frankly there isn’t a lot of strong evidence for that. When this was set low, the I/O balance on the array (and from a host) was usually almost perfectly balanced across the paths. When a path failed due to some physical failure along that path (switch, HBA, port, cable, etc) ESXi would fail that path much more quickly leading to less disruption in performance during the failure The reason we (Pure) recommended the change down to switching paths after every single I/O was for two many reasons: By changing what was called the I/O Operations Limit (sometimes called the IOPS value) you could realize a few additional benefits. The other option was to change paths after a certain amount of throughput, but frankly, very few went down that route.Ī popular option for tuning RR, was to increase the path switching frequency. So for a given device it would use one path for 1,000 I/Os, then the 1,001st I/O would go down a different path. The default configuration of RR was to switch logical paths every 1,000 I/Os for a given device. Round Robin was a great way to leverage the full performance of your array by actively using all of the paths simultaneously. This is VMware’s built-in path selection policy for arrays that offer multiple paths. Why was this PSP option introduced? Well the most common path selection policy is the NMP Round Robin. So what is it? Well first off, see the official words from my colleague Jason Massae at VMware here: In reality, this option was introduced in the initial release of 6.7, but it was not officially supported until update 1. This is my first (but certainly not last post) on the new path selection policy option in vSphere 6.7 Update 1.
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January 2023
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