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Home > Success Center > Log & Event Manager (LEM) > LEM - Knowledgebase Articles > The Reason why LEM Needs Memory and CPU Resource Reservations

The Reason why LEM Needs Memory and CPU Resource Reservations

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Updated: September 28, 2018


This write-up explains why LEM needs memory and CPU resources set in the form of reservations.


All versions of LEM


LEM requires resource reservations in the form of CPU and RAM, just as other appliances like routers and firewalls have 'dedicated' resources. 

LEM handles traffic in real-time, receiving and normalizing data, firing rules when a specific type of data is received, displaying data in the console, pushing data into the database, allowing nDepth searches for that data, and allowing the Reports application to retrieve data from the database. A lot of the communication that makes this happen is Java based, and because of the way LEM utilizes memory, it needs more RAM that other devices and cannot allow other VM's to take the memory in use by LEM. In addition, LEM commonly receives a constant stream of log data from multiple sources, so there is very little recovery time for LEM to 'catch up'. LEM is very unique in how it operates and the different types of data received, so reservations of memory and CPU are critical.


By the nature of virtualization, all VM administrators want to share resources and not dedicate the resources. Unfortunately, because of what LEM does, memory and CPU reservations are critical to keeping the LEM running correctly.  And LEM is unique enough, that viewing the performance measures in VMware or Hyper-V, does not always give a clear indication whether LEM needs more or less reservations. The need for more reservations is based primarily on the volume of traffic received, but also on configurations set in LEM, or the type of data received.

While a shortage of RAM can cause excessive swapping and balooning, or out of memory errors, it's still possible to experience instability, performance problems and even filesystem corruption. In VMware, always set the CPU limits and RAM limits to match the reservations. In Hyper-V, always use the 100%/100%/100% or the slider bars set to maximum, so that the the reservations match the allocations/limits.

The following chart is a guideline for setting reservations, but it is very dependent upon the type of traffic and the configurations set in LEM. The number of CPU's can vary, depending upon the type, date and technologies used by the manufacture. In addition, the storage speed would need to be sufficient to handle the traffic. VM administrators can help in this area, and Solarwinds support can run some speed tests to verify the speed as well.

    < 15   million  Events-Per-Day               8GB Ram         2-CPU @2Ghz 
  15-35   million  Events-Per-Day       10-16GB Ram        4-CPU @2Ghz  
  35-60   million  Events-Per-Day       20-32GB Ram        6-CPU @2Ghz
  60-90   million  Events-Per-Day       32-48GB Ram       8-CPU @2Ghz
  90-120  million Events-Per-Day     48-64GB Ram      10-CPU @2Ghz
120-150 million Events-Per-Day     64-96GB Ram       12-CPU @2Ghz
150-200 million Events-Per-Day     96-128GB Ram     14-CPU @2Ghz


These links are essential to understanding LEM:


Additional Links:

  • Full memory reservation eliminates ballooning or hypervisor swapping leading to more predictable performance with no latency overheads due to such mechanisms.  For more information, click here. (© 2013 VMware, Inc., available at, obtained on May 4, 2016.)

  • Set the memory reservation value in the VMware Infrastructure Client to the size of memory for the virtual machine. To read more, click here.   (© 2013 VMware, Inc., available at, obtained on May 4, 2016.)

  • Without memory reservation, vSphere may reclaim memory from the VM, when the host free memory gets scarce. See more here. (© 2013 VMware, Inc., available at, obtained on May 4, 2016.)

  • If a performance-critical virtual machine needs a guaranteed memory allocation, the reservation needs to be specified carefully because it may impact other virtual machines. Visit ""  to read more. (© 2013 VMware, Inc., available at, obtained on May 4, 2016.)


Using the VM performance metrics to define what is needed for the LEM will not help keep the LEM running. Without reservations, the virtual appliance will have stability issues and performance problems, and expect the LEM to go down periodically.

Disclaimer: Please note, any content posted herein is provided as a suggestion or recommendation to you for your internal use. This is not part of the SolarWinds software or documentation that you purchased from SolarWinds, and the information set forth herein may come from third parties. Your organization should internally review and assess to what extent, if any, such custom scripts or recommendations will be incorporated into your environment.  You elect to use third party content at your own risk, and you will be solely responsible for the incorporation of the same, if any.

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