Have you ever noticed the dash lines on the "Availability" Azure Monitor metric for your Storage Account? What's that about? Is your Storage Account down?
Why is it that we see sections where there is a dashed line and other sections where there is a solid line?
Well, it turns out that Azure metrics charts use dashed line style to indicate that there is a missing value (also known as “null value”) between two known time grain data points. Meaning, this behavior is by design, yes, by design. It is useful for identifying missing data points. The line chart is a superior choice for visualizing trends of high-density metrics but may be difficult to interpret for the metrics with sparse values, especially when corelating values with time grain is important.
The dashed line makes reading of these charts easier but if your chart is still unclear, consider viewing your metrics with a different chart type. For example, a scattered plot chart for the same metric clearly shows each time grain by only visualizing a dot when there is a value and skipping the data point altogether when the value is missing, for my case this is what I get just after selecting the scatter chart:
So, by using the scatter chart is a lot clearer now where are the missing data points. But why would there be any missing data point for the "Availability" Azure Monitor metric in the first place?
Well, it turns out that the Azure Storage Resource Provider only reports the Availability data to Azure Monitor when there is ongoing activity, meaning, when the Storage Resource Provider is processing requests on any of its services (blob, queue, file, table). If you are not sending any requests to your Storage Account, you should expect the "Availability" Azure Monitor metric to show big sections of dashed lines and understand that this is by design.
This is critical because if you don't know this, you may think that the following chart shows that your Storage Account has been "unavailable" for several hours:
However, by taking a look at the scatter chart, we know now that there was a lot of inactivity on this Storage Account, and that at some point only 1 datapoint was showing "no availability", after which there was also an important gap again reflecting a period of no activity, for the Storage Account to then start receiving requests and for the "Availability" Azure Monitor metric to show 100% again:
Chart shows dashed line