log file size
Guessing Game – Planning & Sizing SIEM Based on EPS
Many of the competing log management and SIEM tools on the market these days use some variation 0f the Events Per Second (EPS) metric to determine the licensing, sizing and storage requirements for scalable solution. Unfortunately, none of the devices that are to be monitored have a specification associated with the amount of logging which will be generated per second (or volume for day, for that matter!) by the device. Moreover, many of the same device type from the same vendor will generate varying amounts of log volume daily and it’s more of an art than a science when determining what the total volume all of the corporate devices will generate daily.
Determining EPS isn’t a problem for existing log management or SIEM customers looking to upgrade to a new solution as they can generate reports from the old log management/SIEM tool and provide a break-down of device type and the daily volumes generated by each device category. However, prospects looking for a proposal for a net-new solution are plagued with the following tasks to properly design a log management or SIEM solution:
- Complete inventory of all assets they plan on monitoring
- Determining average, sustained event rates expressed as an EPS metric
- Understanding how logging levels impact the volume of logs that are generated
- Retention periods, storage options, use cases, regulatory requirements, ad infinitum
Fortunately, once you have a device count and can determine the EPS generated on average by each of the different device categories you need to monitor, the math is easy to determine the licensing, storage, system performance and archiving needs. My post “Basic Log Storage Calculations” http://www.netcerebral.com/?p=208 can assist in the sizing, as this post is geared more towards guessing the EPS averages for each device types.
In my roles as a presales SE that sold log management and SIEM we often were asked by prospects for budgetary quotes, proposals and architecture with little to no empirical data. In most cases the best we could get out of the prospect is an itemized inventory of the number and types of systems they would like to monitor. Without an understanding of the log volumes generated by devices, unique to every customer’s environment, we had to come up with a system of determining the EPS for the different device classes and using this as a starting point for calculating daily storage (EPS * Event_Size * 84600 / Compression Ratio).
The list below is an example of lessons learned in the field from actual customer environments and a document provided by SANS (sponsored by NitroSecurity – now McAfee) called “Benchmarking Security Information Event Management (SIEM)” (found at http://www.sans.org/reading_room/analysts_program/eventMgt_Feb09.pdf). With the information we collected we devised a list, which is a cross-section of averages per event source.
I hope you find this helpful: