How to Monitor Bandwidth Throttling

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Article ID: 238145 - View products that this article applies to.
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SUMMARY

When you enable bandwidth throttling, Internet Information Services (IIS) activates a set of counters to monitor it in System Monitor (SysMon). These counters can be identified by "Async I/O" in the counter name. These counters are active only when bandwidth throttling is enabled. (If bandwidth throttling is not enabled, the counters appear in SysMon, but they always have a value of zero.)

MORE INFORMATION

The Async I/O counters are part of the Internet Information Services Global performance object. They represent totals for all of the IIS services. Bandwidth is not measured for each service. The following table lists and describes the Async I/O counters.

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CounterIndicates
Internet Information Services Global: Current Blocked Async I/O RequestsThe number of requests blocked (that is, held in a buffer until bandwidth is available) by bandwidth throttling as reported during the most recent observation.
Internet Information Services Global: Total Allowed Async I/O RequestsThe number of requests allowed by bandwidth throttling since the service was last started.
Internet Information Services Global: Total Blocked Async I/O RequestsThe number of requests blocked (that is, held in a buffer until bandwidth is available) by bandwidth throttling since the service was last started.
Internet Information Services Global: Total Rejected Async I/O RequestsThe number of requests rejected by bandwidth throttling since the service was last started.
Internet Information Services Global: Measured Async I/O Bandwidth Usage/MinuteThe number of bytes sent per minute as indicated by a sample taken by bandwidth throttling.

The bandwidth setting determines whether IIS accepts or rejects a request for a static HTML page, based on periodic samples of the rate at which bytes are sent on the server.

If the bandwidth used (as indicated by the sample) approaches the maximum set by the user, bandwidth throttling blocks read requests, but allows write requests and transmission requests. Read requests are blocked first, because they are likely to result in further requests.

If the bandwidth used exceeds the maximum set by the user, bandwidth throttling rejects read requests, blocks large write requests and transmission requests, and allows small write requests and transmission requests.

To determine how many requests are being blocked and rejected, monitor the Async I/O counters. These counters display cumulative totals, so it's best to use the SysMon log to log the counter values. A spreadsheet can also be used to calculate the rate over time. SysMon can be used to notify administrators when the number of blocked or rejected requests exceeds a threshold.

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Article ID: 238145 - Last Review: December 3, 2007 - Revision: 3.4
APPLIES TO
  • Microsoft Internet Information Services 6.0
  • Microsoft Internet Information Services 5.0
  • Microsoft Internet Information Services 7.0
Keywords: 
kbinfo KB238145

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