Auto Image Replication (AIR) jobs can exhibit slow performance particularly when copying smaller images. It will take a minimum of 30 seconds per image to replicate an image from the source domain to the target domain. This imposes a daily throughput limit of 2880 images for each replication channel.
There are no errors conditions or error messages associated with this problem. The most likely symptom is a growing backlog of images to be replicated because more images are created than can be processed in a given period
The cause of the performance issue is the time needed to detect when the replication operation is complete. When replicating large images, this time factor is very short related to the time needed for the replication itself and is not noticeable. When replicating small images, the time factor can be much longer than the time needed for the replication and becomes very significant.
Contact NetBackup Technical Support to obtain a code fix for the problem. Request the following EEB depending on the installed NetBackup release level:
- ET3970372 (Release 7.7.3)
- ET3973718 (Release 8.1.1)
- ET3975728 (Release 220.127.116.11)
The EEB will improve the algorithm used to detect that the replication operation is complete. The algorithm behavior can be affected by the average image size, bandwidth available to replicate images, general system activity level, and other factors. The algorithm can be tuned using two NetBackup configuration parameters to optimize results for a given environment. Increasing the accuracy of the replication completion does generate more NetBackup overhead activity and may impact overall performance of the media and storage servers associated with the replication operations.
The parameter values can be changed using the NetBackup nbsetconfig command. The two parameters represent two different ways to tune the algorithm by setting the time factor used to detect replication completion. Only one of the parameters should be used. Determining the optimum value for either parameter can best be determined by trial and error.
Use the nbsetconfig command to set the time factor is a fixed value:
AIR_POLL_INTERVAL_TIME = <seconds>
This option sets the time factor to a fixed number of seconds and should be used when it's desirable to optimize the time needed to complete the replication. It will generate the most overhead. Use this option with an initial value of 1 to minimize the time needed and increase the the throughput. Increase the value if the overhead generated impacts system performance.
Use the nbsetconfig command to set an average image size:
AIR_POLL_INTERVAL_CHUNK_SIZE = <size_value>
This option attempts to calculate the best time factor based on image size. The goal is to set the time factor to approximate the time it will take to replicate a typical image. The size value should be a decimal number representing the number of bytes that can be replicated in 1 second. The default value is 104857600 (100 megabytes). Increasing the chunk size value will decrease the time factor. This will improve the accuracy of the completion detection at the cost of increased overhead.
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