Month: May 2011

Background

This article explains how to determine whether an ExacqVision server’s hardware has been overloaded, how ExacqVision software manages the overload, and how to address the root cause.

Video recording and retrieval can place a significant load on a server’s data storage subsystem. This load can be highly variable on systems configured for motion-based recording or with cameras that have variable bit rates. Video searches also place a large, short-term load on the storage system during retrieval.

When the server’s storage is unable to read and write data at the rate determined by the cameras and user searches, data writes are queued in physical memory. Although this is a useful feature for short-duration overloads, longer or more consistent overloads exhaust the memory available to the ExacqVision Server software.

ExacqVision software (version 4.6.5 and above on Windows, 4.6.10 and above on Linux) contains an overload management feature. This feature enables the server to continue operating with degraded write performance. During periods of server storage overloads, ExacqVision Server software pauses recording of all cameras to allow the storage system to catch up. An overload is defined as either of the following situations:

1. Less than one eighth of the physical memory is available.
2. ExacqVision’s committed virtual memory exceeds half the available virtual memory space.
   

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Testing

The following test should be performed on systems that might be experiencing overloads:

a.  On the Client Configuration screen, select the server from the site tree.

b.  On the System Log tab, set the system log level to Warning, and enter a long search period. Click Search.

c.  In the search box, enter the word “throttling”

d.  A “throttling video” message indicates the first occurrence of video throttling. A subsequent “not throttling video” occurs 60 seconds after the last throttling activity.

See Also: How do I monitor Disk I/O?

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Corrective Actions

1. Lower the frame rate or quality on cameras until the memory usage does not increase significantly during searches.<br><br>
2. Install an additional server, transferring some of the cameras from the overloaded server.<br><br>
3. Install a higher-performance disk system in the existing server.<br><br>
4. (LEGACY) 32-bit Windows only: If the server has less than 4GB of RAM, you can install additional memory to help with short-term overloads (such as multiple simultaneous searches). However, this will not correct systematic overloads (too much steady camera video). Memory in excess of 4GB typically produces little or no delay in the onset of video throttling, although it could be helpful in 64-bit Windows.
   

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