This issue is observed when a user tries to upload a large file to the server behind F5. The user faces slowness while uploading the file first which afterward gets failed, F5 shows an unusual behavior as other virtual servers also face the same issue while uploading files.

Understanding more about how BIGIP handles file upload requests:

K01235989: Understanding BIG-IP ASM large file upload behavior.

In such cases, a user is indeed hitting a limit on the number of long request buffers on the system and should look to increase the number of long request buffers.

There are three ways to increase the number of long requests buffers on the system:

1. Increase the amount of memory available to ASM’s bd process
– This can be done with reprovisioning, and can also be done with an ASM system variable (total_umu_max_size) change.

2. Increase the percentage of bd memory available to handle long requests
– This is done by changing an ASM system variable (long_request_mem_percentage); increasing the number of request buffers significantly and quickly, is the best option.

3. Decrease the size of the long request buffers
– This is seldom done.

How to change the long_request_mem_percentage: ( K11434152 article on AskF5)

1. Log in to the BIG-IP ASM command line.

2. Specify the percentage of the memory allocated for long requests by modifying the long_request_mem_percentage variable. To do so, use the following command syntax:

/usr/share/ts/bin/add_del_internal add long_request_mem_percentage <percentage value>

3. Restart the asm process by typing the following command:

tmsh restart /sys service asm

This will cause a brief traffic disruption while bd is restarted, so should preferably be done during a maintenance window. It’s recommended to increase the long_request_mem_percentage to 30 however, after reprovisioning the memory the issue usually gets resolved and the percentage value of long_request_mem_percentage can be decreased to minimal.