Microsoft.ElasticSan/elasticSans: ElasticSanProvisionedBase returns 0 at documented PT1M grain, only PT30M has data

Start by reproducing the reported values through the ARM metrics endpoint and metrics:getBatch for ElasticSanProvisionedBase at PT1M and PT30M. Compare the results with the linked Microsoft.ElasticSan/elasticSans supported-metrics reference; done means establishing the supported grain or confirming the documentation needs correction.

Summary

ElasticSanProvisionedBase (Capacity category, Microsoft.ElasticSan/elasticSans) is documented with Time
Grains including PT1M, but querying it at PT1M consistently returns 0 for every bucket. Querying the
exact same metric, same resource, same moment, at PT30M returns the correct non-zero value.

Evidence

Repeated polling (every ~30s, over a 16 minute window) against a real Elastic SAN resource, via both the
ARM metrics API and the batch metrics API:

Source   Aggregation@Grain    Buckets  Populated  Value
ARM      Maximum@PT1M         30       30         0
Batch    Maximum@PT1M         30       30         0
ARM      Maximum@PT30M        2        2          26,388,279,066,624
Batch    Maximum@PT30M        2        2          26,388,279,066,624

This pattern repeated at every poll in the window: PT1M never returned a non-zero value, PT30M always
did. It was identical between the ARM metrics endpoint
(.../providers/Microsoft.Insights/metrics?api-version=2019-07-01&...&interval=PT1M) and the batch metrics
endpoint (metrics:getBatch?api-version=2024-02-01&...&interval=PT1M), so it isn't specific to one API path.

Question / Ask

Is PT1M actually a supported grain for this metric, or does the platform only compute/refresh
ElasticSanProvisionedBase on a longer cadence (e.g. 30 minutes) regardless of what grain is requested? If
it's the latter, could the supported-metrics reference for
Microsoft.ElasticSan/elasticSans
be corrected — it currently lists PT1M as the only Time Grain for this metric, which doesn't match what we
observe.

Environment

Queried directly via the ARM Metrics REST API and the batch metrics API (metrics:getBatch), not through
any client library.