Guide to LUN configuration and virtualisation
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Server virtualization can conserve energy and money while increasing overall efficiency, but when certain VMs use too much I/O bandwidth, it can negatively affect the performance of other VMs sharing the same storage resources. With vSphere Storage I/O Control, managers can regulate VM storage usage, improving overall performance and ensuring the most important data gets the bandwidth it needs. In this video, Howard Marks discusses the specifications and benefits of Storage I/O Control, which is included with the Enterprise Plus edition of vSphere.
One of the problems with virtualization is that we have noisy neighbors. My favorite noisy neighbor example was a large bank that called me and said they were having some difficulty with their backups. … They said when they run their backups, the users in Hong Kong can't access the intranet portal anymore. I… looked at what they were doing, and I discovered that they had very carefully managed their backup system so that they thought they were backing up servers spread across multiple virtual server hosts using a backup agent in each guest. The backup group had spent a lot of time doing analysis of what VMs ran on what virtual server host at any given time, when they set up the backup schedule. However, the VMware guys had several weeks later turned on DRS [Distributed Resource Scheduler], so the guests had moved. At 3:00 in the morning New York time, seven guest jobs all triggered off at the same time, and five of those guest jobs were on the same host. And lo and behold, the Web server for the portal in traditional Chinese that the users in Hong Kong were accessing was on that host, too. The backup guys were smart enough to say, "Back up the Hong Kong facing host at 4:00 in the morning," but if you back up five VMs on the same host as that one, it's starved for network bandwidth, and the users cannot get to it either. Just as you can have noisy neighbors who are eating your network bandwidth, you can have noisy neighbors who are eating your storage bandwidth.
With Storage I/O Control, I can do quality of service for VMFS [Virtual Machine File System], so I can say, "Per data store, when the latency on a particular VM exceeds some limit, start throttling that VM back. Don't give it as many IOPS as it is asking for; give it fewer. Make it a less noisy neighbor. Let those resources be available for some of the better-behaved neighbors." We have all lived in an apartment near frat boys and it is just not fun, and this is better than calling the cops. Again, it is a feature only available in [vSphere] Enterprise Plus. It's only for block storage; it only works on LUNs that have one extent, and, of course, it doesn't work for RDMs [raw device mappings] because it's managing storage network traffic that RDMs are bypassing by going around it.
[As an example], we've got two servers -- and I don't know how many of you have ever run Iometer, but Iometer is a common benchmark. … We run two guests, and when we run the two guests, they both … get about the same amount of I/Os, and there's about 3,500 total I/Os. When we then throttle one back and … say, "You should only get about 600 I/Os," the other one gets substantially more, and so it responds in a matter of seconds. If you are actually running Enterprise Plus, Storage I/O Control is strongly recommended.