vSAN performance questions - How do I identify if I have bad performance?
This question came in this morning.
๐๐บ ๐๐๐๐ฆ ๐ค๐ญ๐ถ๐ด๐ต๐ฆ๐ณ ๐ช๐ด ๐ด๐ญ๐ฐ๐ธ, ๐ข๐ฏ๐ฅ ๐ ๐ต๐ฉ๐ช๐ฏ๐ฌ ๐ช๐ต'๐ด ๐ฃ๐ฆ๐ค๐ข๐ถ๐ด๐ฆ ๐ ๐ฏ๐ฆ๐ฆ๐ฅ ๐ต๐ฐ "๐ฐ๐ฑ๐ต๐ช๐ฎ๐ช๐ป๐ฆ ๐ต๐ฉ๐ฆ ๐ฅ๐ณ๐ช๐ท๐ฆ๐ด, ๐ฅ๐ฐ ๐บ๐ฐ๐ถ ๐ฉ๐ข๐ท๐ฆ ๐ข ๐จ๐ถ๐ช๐ฅ๐ฆ ๐ง๐ฐ๐ณ ๐ต๐ฉ๐ช๐ด?
From time to time I see various performance related questions and they often start with some common issues:
1. They fail to identify WHY they think there is a problem with the back end.
2. They fail to demonstrate understanding of what a performance problem looks like.
So rather than directly respond to this question, we will look at how to identify if a performance problem is not actually present (or not at the storage layer).
Next up we might ask the person who asked us this?
So why do you think it's slow?
docs.vmware.com/en/VMware-vSphโฆ
Should I measure performance usage in throughput or IOPS?
Which test should I use for testing my cluster?
How do I know what my apps/users are using?
While some application vendors offer general guidance on their block size usage, they may not truely reflect all uses of the application or how the data is coalcesed and sent to disk by the operating system and in guest file system. VMware vSAN I/O Insight will actually let you capture this (and a ton of other stuff). Here is a short demo video duncan shows that includes graphs for block size as well as read/write mix. Remember writes are commonly more difficult to process than reads by storage systems.