Merge pull request #21847 from fsautomata/patch-9

IoT Hub - clarify device connection throttle

articles/iot-hub/iot-hub-devguide.md

@@ -576,6 +576,11 @@ The following is the list of enforced throttles. Values refer to an individual h
 | Cloud-to-device sends | 100/min/unit |
 | Cloud-to-device receives | 1000/min/unit |
 
+It is important to clarify that the *device connections* throttle governs the rate at which new device connections can be established with an IoT hub, and not the maximum number of simultaneously connected devices. The throttle is dependent on the number of units that are provisioned for the hub.
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+For example, if you buy a single S1 unit you get a throttle of 100 connections per second. This means that to connect 100,000 devices it takes at least 1000 seconds (approximately 16 minutes). However, you can have as many simultaneously connected devices as you have devices registered in your device identity registry.
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 **Note**. At any given time, it is possible to increase quotas or throttle limits by increasing the number of provisioned units in an IoT hub.
 
 **Important**: Identity registry operations are intended for run-time use in device management and provisioning scenarios. Reading or updating large number of device identities is supported through [import/export jobs](#importexport).