Technical Tip: Higher base memory usage after upgrade of FortiOS 7.2.x to 7.4.8

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Description	This article describes why a higher base memory usage is observed after upgrading to FortiOS 7.4.8.
Scope	FortiGate v7.4.8.
Solution	The base memory usage on FortiOS 7.4.8 GA is higher than compared with a FortiOS 7.2.x release. This means that the memory allocated by the operating system per default and without any traffic or features being enabled is higher. This is expected behavior due to several design changes, new features and security solutions being added in version 7.4.x. One of the reasons is the relocation of IPS shared memory databases from the /data2 to the /tmp filesystem. In FortiOS 7.4.8 different databases, like for example the ISDB and GEODB, will be cached in the /tmp filesystem. As a result, the system will allocate more than 100MB of additional memory on 7.4.8 compared to previous firmware releases like on 7.2.11 GA. This change was implemented to avoid issues with high CPU load in iowait when storing IPS shared memory on the flash disk. Several memory optimizations will be completed in 7.4.9 GA. On lower firmware releases it is recommended to optimize the memory usage according to different knowledge base articles: Troubleshooting Tip: How to optimize memory usage specifically for FortiGateRugged-60F low-end model...  Technical ip: Free up memory to avoid conserve mode  Technical Tip: Low-end FortiGate models with RAM ≤ 2GB entering conserve mode due to increased ISDB ...  Some examples showing the increase of memory between firmware versions 7.2.11 and 7.4.8. FortiGate-101F with 4GB memory with a basic configuration and no traffic FortiGate-101F v7.2.11,build1740,250210 (GA.M) : 27% base memory usage: Memory: 3701336k total, 1001012k used (27.0%), 2432724k free (65.7%), 267600k freeable (7.3%) FortiGate-101F v7.4.8,build2795,250523 (GA.M): 40.7% base memory usage: Memory: 3701276k total, 1506572k used (40.7%), 1875216k free (50.7%), 319488k freeable (8.6%) This is approximately and increase of 13% compared to 7.2.11 GA. FortiGate-101F with 4GB memory and a customer configuration applied and no traffic. FortiGate-101F v7.2.11,build1740,250210 (GA.M): 45% base memory usage: Memory: 3701336k total, 1660980k used (44.9%), 1774772k free (47.9%), 265584k freeable (7.2%) FortiGate-101F v7.4.8,build2795,250523 (GA.M): 55% base memory usage: Memory: 3701276k total, 2044724k used (55.2%), 1337016k free (36.1%), 319536k freeable (8.7%) This is approximately an increase of 10% compared to 7.2.11 GA.