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The File I/O Performance Monitor
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The File I/O Performance Monitor |
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hIOmon™ FAQs - hIOmon™ Presentation Client |
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The following Frequently-Asked-Questions (FAQs) relate to the operation and use of the hIOmon™ Presentation Client; the answers follow below: P-Q1. I just completed installing hIOmon and tried to start the hIOmon Presentation Client. Instead of seeing the initial hIOmon Presentation Client display, I get WinZip (or some other zip utility) showing a bunch of files. What's wrong? P-Q2. I just completed installing hIOmon and tried to start the hIOmon Presentation Client. I am getting a hIOmon Presentation Client error message display complaining about some kind of "transport error". What's wrong? P-Q3. I just completed installing hIOmon and started the hIOmon Presentation Client. The "Selected hIOmon Manager" drop-down boxes in all of the hIOmon Presentation Client displays are empty. Should they be empty? P-Q4. The hIOmon Presentation Client has successfully connected to the hIOmon Manager, but I do not see any file I/O operation performance information in either of the "real-time" views (i.e., neither the "File I/O Operation Trace" nor the "File I/O Performance Summary" views). What's wrong? P-Q5. The hIOmon Presentation Client has successfully connected to the hIOmon Manager, but I get an error message when I try to activate the retrieval of "real-time" statistics (for either the Trace and/or the File I/O Summary views). What's wrong? P-Q6. A note indicating that "High precision time duration recording of I/O operation event statistical data is NOT enabled" or that "Unable to determine time duration of I/O operation due to inadequate timing precision" has appeared within the "File I/O Operation Trace" and/or "File I/O Performance Summary" displays while viewing the file I/O operation performance information (for either the real-time or replay display modes). What do they mean? P-Q7. A note indicating that "Missing I/O Operation event data due to insufficient buffer space in the hIOmon I/O Monitor" has appeared within the "File I/O Operation Trace" and/or "File I/O Performance Summary" displays while viewing the file I/O operation performance information (for either the real-time or replay display modes). What does this note mean? P-Q8. Sometimes while viewing the file I/O operation performance information (either "real-time" or "replay" display modes, and for either the "File I/O Operation Trace" and/or the "File I/O Performance Summary" displays), the hIOmon Presentation Client seems to "stall" (that is, there appears to be a somewhat prolonged delay before the display is updated with newer file I/O operation performance information). What's causing these delays? P-Q9. Can I use the hIOmon Presentation Client to view file I/O operation performance information in a "replay" mode display while the hIOmon Manager is concurrently saving (to a "File I/O Log" disk file for subsequent "replay" mode display) the file I./O operation performance that it has just retrieved from the hIOmon I/O Monitor? P-Q10 What's the suggested approach for initially defining the filters used to identify the files to be monitored? P-Q11 The idle time percentage calculated/displayed by hIOmon is greater than 100%. How can that happen? P-Q12 The idle time percentage calculated/displayed by hIOmon seems lower than expected, based upon the associated number of file I/O operations performed and their response times. For example, an idle time percentage of only 10% is displayed when the hIOmon I/O Monitor observed (during a 12 millisecond time period) two file I/O operations both performed with sub-millisecond response times. How can that happen? hIOmon Presentation Client Operation and Use P-Q1. I just completed installing hIOmon and tried to start the hIOmon Presentation Client. Instead of seeing the initial hIOmon Presentation Client display, I get WinZip (or some other zip utility) showing a bunch of files. What's wrong? P-A1. This can occur when the .jar file extension type has been associated with your zip utility program instead of the Java Runtime Environment (JRE). The hIOmon Presentation Client is contained within a jar file and if the .jar file extension type is associated with a zip utility, then the zip utility will be invoked (instead of the JRE) resulting in a display of the file contents of the jar file. Normally the .jar extension is associated with the "javaw.exe" so that when you "open" a .jar file, it invokes the "javaw.exe -jar" association. You might want to take a look under the "Folder Options" and the "File Types" tab to see what options are set for the "Executable Jar File" type; it should show for the "open" action that "javaw.exe -jar" is invoked for this file type. If you don't want to change the file type association, you can as one workaround open a DOS command-prompt window, go to the directory where the hIOmonPC.jar is located and then enter: javaw -jar hIOmonPC.jar P-Q2. I just completed installing hIOmon and tried to start the hIOmon Presentation Client. I am getting a hIOmon Presentation Client error message display complaining about some kind of "transport error". What's wrong? P-A2. If you are getting, for example, a "HIOMmsgTransportOpen: error code = 30" error when you try to start the hIOmon Presentation Client, then this usually means that the hIOmon Manager is not running. If the hIOmon Manager service is not running, then the hIOmon Presentation Client will encounter a "message transport error" when it tries to communicate with the hIOmon Manager. Please be sure that the hIOmon software installation process was successfully completed; see "question 2" within the "Installation FAQ" help information for additional details. Also, please check the System Event Log "Application Log" for the results of the hIOmon software installation process; entries will be added by the hIOmon software installation process to record various failure/success events related to the installation. In addition, please note that the hIOmon Manager generally records a "successfully started" Event Log entry each time it is started as further confirmation that it has been successfully activated. P-Q3. I just completed installing hIOmon and started the hIOmon Presentation Client. The "Selected hIOmon Manager" drop-down boxes in all of the hIOmon Presentation Client displays are empty. Should they be empty? P-A3. When the hIOmon Presentation Client is first started after the installation of the hIOmon software, the hIOmon Presentation Client will try to automatically connect to the hIOmon Manager running upon the same computer as is the hIOmon Presentation Client; please refer to the "Presentation Client Configuration Initialization" description within the hIOmon User Guide for more information. You can manually connect to desired hIOmon Manager(s) using any of the hIOmon Presentation Client menu displays that feature a "Selected hIOmon Manager" box at the top of the display. Simply enter, within the "Selected hIOmon Manager" box, the name (or IP address) of the particular computer server upon which the desired hIOmon Manager is running. Be sure to hit the "enter" key on the keyboard after you have typed the name (or IP address) within the "Selected hIOmon Manager" drop-down box. A message box will pop up indicating that the hIOmon Presentation Client is trying to connect to the selected hIOmon Manager. You can also set up a "profile" so that the hIOmon Presentation Client will subsequently connect automatically to one or more specified hIOmon Managers when the hIOmon Presentation Client is started; please refer to the hIOmon User Guide for more information about "Profiles". P-Q4. The hIOmon Presentation Client has successfully connected to the hIOmon Manager, but I do not see any file I/O operation performance information in either of the "real-time" views (i.e., neither the "File I/O Operation Trace" nor the "File I/O Performance Summary" views). What's wrong? P-A4. Make sure that you have followed all of the steps outlined in the "Getting Started" help information. Assuming that a Filter Selection is loaded within the hIOmon I/O Monitor, that this Filter Selection includes filters which select the collection of either "Trace Records" and/or "File I/O Summary" performance statistics, that the collection of file I/O operation performance information is active within the hIOmon I/O Monitor, that the generation of records containing the collected file I/O operation performance information is enabled within the hIOmon I/O Monitor, and that there has been some file I/O activity that has matched the filters defined in the loaded Filter Selection, make sure that you have also activated the retrieval of the file I/O operation performance information from the selected hIOmon Manager. A note in bold at the bottom of the "File I/O Operation Trace" and/or the "File I/O Performance Summary" menu display will indicate either "Retrieval active" or "Retrieval stopped". Click on the "Start" button at the bottom of either the "File I/O Operation Trace" or the "File I/O Performance Summary" menu display to start the retrieval of the file I/O operation performance information from the associated hIOmon I/O Monitor via the selected hIOmon Manager. NOTE: For the display of "real-time" file I/O operation performance information, the hIOmon Presentation Client will issue a warning message if a Filter Selection is not currently loaded within the hIOmon I/O Monitor, if the collection of file I/O operation performance information is currently disabled within the hIOmon I/O Monitor, or if the generation of records containing the collected file I/O operation performance information is currently disabled within the hIOmon I/O Monitor. Under these circumstances, you can still click on the "Start" button to start the retrieval of the file I/O operation performance information from the associated hIOmon I/O Monitor (although no file I/O operation performance information will/can be transferred to the hIOmon Presentation Client until a Filter Selection is loaded and/or collection/recording is enabled within the hIOmon I/O Monitor). P-Q5. The hIOmon Presentation Client has successfully connected to the hIOmon Manager, but I get an error message when I try to activate the retrieval of "real-time" statistics (for either the Trace and/or the File I/O Summary views). What's wrong? P-A5. The error message should indicate the specific nature of the problem (e.g., that the hIOmon I/O Monitor associated with the selected hIOmon Manager is not accessible). Make sure of the following:
P-Q6. A note indicating that "High precision time duration recording of I/O operation event statistical data is NOT enabled" or that "Unable to determine time duration of I/O operation due to inadequate timing precision" has appeared within the "File I/O Operation Trace" and/or "File I/O Performance Summary" displays while viewing the file I/O operation performance information (for either the real-time or replay display modes). What do they mean? P-A6. These notes highlight the fact that high-precision I/O operation time duration recording was not enabled at the time the hIOmon I/O Monitor was monitoring the collected file I/O operation performance information. Since the hIOmon I/O Monitor was not monitoring the file I/O operations with the highest timing precision available within the computing system, the precision of the time durations derived for the file I/O operations will be impacted. Under some systems, the timing precision will default to 10 milliseconds (as an example). Consequently, the hIOmon I/O Monitor will only be able to determine the time duration of an I/O operation within an accuracy of 10 milliseconds (with those I/O operations occurring under 10 milliseconds considered to have a time duration of zero and flagged within the "File I/O Performance Summary" display with an asterisk ("*")), P-Q7. A note indicating that "Missing I/O Operation event data due to insufficient buffer space in the hIOmon I/O Monitor" has appeared within the "File I/O Operation Trace" and/or "File I/O Performance Summary" displays while viewing the file I/O operation performance information (for either the real-time or replay display modes). What does this note mean? P-A7. The hIOmon I/O Monitor uses buffers to contain the file I/O operation performance information that it has collected as part of its file I/O operation monitoring process. If the hIOmon Manager does not retrieve the file I/O operation performance information contained within these buffers in a timely fashion, the contents of the buffers can be overlaid by the hIOmon I/O Monitor with more recent file I/O operation performance information. The file I/O operation performance information that is overlaid is consequently considered "lost"; the note above highlights the occurrence of such "lost" file I/O operation performance information. To help avoid such "lost" file I/O operation performance information, the "Monitor Memory" tab of the "Edit -> Setup Options" menu item (from the main hIOmon Presentation Client display) allows you to optionally configure the selected hIOmon I/O Monitor's "buffer memory management". You can use this menu display to change the maximum allowed memory size of an individual buffer used to contain the collected file I/O operation performance information. You can also configure other aspects of the hIOmon I/O Monitor's "buffer memory management", such as the maximum number of buffers allowed to be used concurrently to contain the file I/O operation performance information. See the "Monitor Memory" section of the hIOmon User Guide for additional options and further information. P-Q8. Sometimes while viewing the file I/O operation performance information (either "real-time" or "replay" display modes, and for either the "File I/O Operation Trace" and/or the "File I/O Performance Summary" displays), the hIOmon Presentation Client seems to "stall" (that is, there appears to be a somewhat prolonged delay before the display is updated with newer file I/O operation performance information). What's causing these delays? P-A8. Assuming that there is file I/O operation performance information awaiting transfer to the hIOmon Presentation Client from the selected hIOmon Manager, these delays are often caused by the Java "garbage collection phenomenon". That is, the Java Virtual Machine (upon which the hIOmon Presentation Client runs) periodically takes higher priority to collect unused memory for subsequent use by the hIOmon Presentation Client. It is often during this "garbage collection" process performed by the Java Virtual Machine that the hIOmon Presentation Client appears to "stall". Another cause for an apparent "stall" is the time required by the Java Virtual Machine to load and display "Tool Tip" help information; see the hIOmon Presentation Client "Tool Tips" Help menu item (select the "Help -> Info -> Tool Tips" menu item from the initial hIOmon Presentation Client display window) for more information about the "Tool Tip" feature. P-Q9. Can I use the hIOmon Presentation Client to view file I/O operation performance information in a "replay" mode display while the hIOmon Manager is concurrently saving (to a "File I/O Log" disk file for subsequent "replay" mode display) the file I./O operation performance that it has just retrieved from the hIOmon I/O Monitor? P-A9. Yes. Both the hIOmon Presentation Client and the hIOmon Manager provide significant support for concurrency. As examples, the hIOmon Presentation Client can concurrently support connections to multiple hIOmon Managers; likewise, the hIOmon Manager can support multiple hIOmon Presentation Client connections (and the concurrent transfer of file I/O operation performance information from multiple File I/O Log files for "replay" mode displays). Such concurrency is essentially limited to the particular licensing options purchased. For example, the hIOmon Presentation Client supports connection to more than one hIOmon Manager at a time up to the maximum number allowed by the particular licensed version of hIOmon; similar licensing limitations exist for concurrent support of hIOmon Presentation Clients by the hIOmon Manager. P-Q10. What's the suggested approach for initially defining the filters used to identify the files to be monitored? P-A10. Attempting to monitor and view a large amount of I/O trace information in real-time mode can degrade system performance (especially if the hIOmon Presentation Client is being run upon the same system that is being monitored by hIOmon). Instead, and as a first step, use the hIOmon filters and summary capabilities (particularly the alert and file close options, along with the ability to arrange the summarized file I/O operation performance information in a particular order) to begin your observations of file I/O operation performance from the overall perspective (i.e., a "top-down" approach). Then, based upon the file I/O operation performance information results provided by hIOmon, drill-down if necessary to the particular files of interest. Using the hIOmon "replay mode" facility can also aid performance as well as allow the ability to (repeatedly) study at a later time the file I/O operation performance information collected by hIOmon. P-Q11. The idle time percentage calculated/displayed by hIOmon is greater than 100% How can that happen? P-A11. The "Idle time percentage" represents the percentage of time observed by the hIOmon I/O Monitor in which there were neither file I/O operations in process nor any file I/O operations queued. For file summaries, the time period covered by this percentage starts with the first file I/O operation access to the file monitored by the hIOmon I/O Monitor until the time that the performance metrics are offloaded by the hIOmon I/O Monitor. For device summaries, the time period covered by this percentage starts when the filters (which specify the particular files/devices that are to be monitored by hIOmon) are activated (or re-activated) within the hIOmon I/O Monitor for the respective device until the time that the performance metrics are offloaded by the hIOmon I/O Monitor. When the high-precision time duration recording option is enabled within the hIOmon I/O Monitor, the "idle time percentage" may exceed 100% as a result of the accumulated idle time value (the numerator) exceeding the overall time period value (the denominator as described above). Both the idle time and overall time period values calculated by the hIOmon I/O Monitor are subject to an anomaly associated with the "Performance Counter" API provided by the Microsoft Windows operating systems (see "PRB: Performance Counter Value May Unexpectedly Leap Forward (Q274323)" within the Microsoft Knowledge Base; see also Q896256 within the Microsoft Knowledge Base). The hIOmon I/O Monitor attempts to correct for these anomalies, but in some cases this correction will be applied to the idle time value without the overall time period value also receiving the benefit of correction (in which case, the idle time value can exceed the overall time period value such that the idle time percentage will consequently exceed 100%). If the idle time percentage exceeds 100%, simply disregard and ignore the idle time percentage value. At the next opportunity, the hIOmon I/O Monitor will subsequently attempt to adjust the overall time period value so that the idle time percentage will once again be valid. P-Q12. The idle time percentage calculated/displayed by hIOmon seems lower than expected, based upon the associated number of file I/O operations performed and their response times. For example, an idle time percentage of only 10% is displayed when the hIOmon I/O Monitor observed (during a 12 millisecond time period) two file I/O operations both performed with sub-millisecond response times. How can that happen? P-A12. When the high-precision time duration recording option is enabled within hIOmon I/O Monitor, the file I/O operation response times and the accumulated idle time value are both calculated by the hIOmon I/O Monitor using the highest precision timing facilities provided by the operating system (which is sub-millisecond timing precision in the case of the various supported Windows platforms). However, the resolution of the standard system timer on these same platforms generally provides a granularity of only about 10 milliseconds. Since the hIOmon I/O Monitor uses the standard system timer (whose granularity is only about 10 milliseconds) to determine the time duration of the period during which it observed the file I/O operations, this "observation" can be off by almost 10 milliseconds. For example, the hIOmon I/O Monitor may retrieve a time stamp from the Windows system timer that indicates 5 minutes and 40 milliseconds after the hour (although the actual time is 5 minutes and 48 milliseconds after the hour). When determining the time duration of the observation period (during which the file I/O operation performance statistics were collected by the hIOmon I/O Monitor), the hIOmon I/O Monitor retrieves a time stamp from the Windows system timer that indicates 5 minutes and 50 milliseconds after the hour (although the actual time is 5 minutes and 52 milliseconds after the hour). Using various algorithms, the hIOmon I/O Monitor attempts to compensate for the limited 10 millisecond granularity of the standard system timer (which again can be off by almost 10 milliseconds); hence, in this example the hIOmon I/O Monitor can calculate a 12 millisecond duration for the observation time period when the actual time duration is only 4 milliseconds. As a result, the "idle time percentage" will be based upon the 12 millisecond observation period (instead of the actual 4 millisecond time duration); this in turn will cause the "idle time percentage" is be lower than expected, especially when just a few file I/O operations with sub-millisecond responses times are observed by the hIOmon I/O Monitor during this observation period. Normally the occurrence of the scenario above is very limited (e.g., is only seen when using the hIOmon Command-Line-Interface (CLI) component to display real-time summarized file I/O operation performance metrics along with observation periods that are less than several 100 milliseconds or so in duration). With observation periods of one second or more, the impact of the limited system timer granularity (of about 10 milliseconds) upon the calculated "idle time percentage" is much less pronounced. |
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hyperI/Osm - improving the performance of storage I/O in computer servers |
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