Memory Usage Thresholds for Health Monitor Alerts
The Memory Usage health module compares memory usage on an appliance to the limits configured for the module and alerts when usage exceeds the levels. The module monitors data from managed devices and from the management center itself.
Two configurable thresholds for memory usage, Critical and Warning, can be set as a percentage of memory used. When these thresholds are exceeded, a health alarm is generated with the severity level specified. However, the health alarm system does not calculate these thresholds in an exact manner.
With high memory devices, certain processes are expected to use a larger percentage of total system memory than in a low memory footprint device. The design is to use as much of the physical memory as possible while leaving a small value of memory free for ancillary processes.
Compare two devices, one with 32 GB of memory and one with 4 GB of memory. In the device with 32 GB of memory, 5% of memory (1.6GB) is a much larger value of memory to leave for ancillary processes than in the device with 4 GB of memory (5% of 4GB = 200MB).
To account for the higher percentage use of system memory by certain processes, the management center calculates the total memory to include both total physical memory and total swap memory. Thus the enforced memory threshold for the user-configured threshold input can result in a Health Event where the “Value” column of the event does not match the value that was entered to determine the exceeded threshold.
Beginning with version 7.4.1, the memory usage health module calculates memory usage by taking into account the free memory available, swap memory available, and buffer cache. To avoid premature memory usage health alerts, it is recommended not to exceed the warning and critical alarm thresholds of 88% and 90%, respectively.
The following table shows examples of user-input thresholds and the enforced thresholds, depending on the installed system memory.
Note | The values in this table are examples. You can use this information to extrapolate thresholds for devices that do not match the installed RAM shown here, or you can contact Cisco TAC for more precise threshold calculations. |
|
User-Input Threshold Value |
Enforced Threshold Per Installed Memory (RAM) |
|||
|---|---|---|---|---|
|
4 GB |
6 GB |
32 GB |
48 GB |
|
|
10% |
10% |
34% |
72% |
81% |
|
20% |
20% |
41% |
75% |
83% |
|
30% |
30% |
48% |
78% |
85% |
|
40% |
40% |
56% |
81% |
88% |
|
50% |
50% |
63% |
84% |
90% |
|
60% |
60% |
70% |
88% |
92% |
|
70% |
70% |
78% |
91% |
94% |
|
80% |
80% |
85% |
94% |
96% |
|
90% |
90% |
93% |
97% |
98% |
|
100% |
100% |
100% |
100% |
100% |