When using heavily the DDP or connecting multiple clients with SMB, NAGIOS might start to send alerts related to the swap usage.
When swap free space reaches 0%, you will receive the following notification:
Notification Type: PROBLEM
Service: Swap Usage
Host: localhost
Address: 127.0.0.1
State: CRITICAL
Date/Time: Mon Feb 13 13:46:35 JST 2017
Additional Info:
SWAP CRITICAL - 0% free (0 MB out of 2536 MB)
When getting this kind of notification, it means that the DDP is starting to lack memory resources, which increases the risk of system crash.
You can resolve this by rebooting the DDP, which will clear both the RAM and swap.
It is possible to check how much RAM is still free by logging to the DDP by ssh and then entering the following command:
free
This command will print information about RAM and swap usage in KB as in the following example:
In the above example, swap is 2597136 KB which is about 2,6 GB big and swap free space is 0 KB.
Also RAM is 16320760 KB big which is about 16 GB and RAM free space is 713096 KB which represents 713 MB.
So in this case, swap is completely full and RAM resources are also almost completely used since there is only 713 MB left out of 16 GB of RAM.
It is recommended to reboot the DDP when the system resources are used as much as in this example.
When swap usage alerts are coming too often, it generally means that SMB is heavily used so it's good reconsidering the workflow and using the DDP drivers as much as possible to avoid resource issues.