Running RC5 on Debian 11 as a guest on KVM with 4 ONVIF (SV3C 3MP). System was very unstable and would run for a few hours and occasionally for as long as a day. On watching the system load it appeared that average load factor was OK around 10-15% but with occasional surges to 100% caused by the soft interrupt handler for the virtual machine. At this point I had a 200 GB LVM volume for the recordings and frequently a video segment would be corrupted midway.
Finally figured it out! For some reason I had set the NIC to rtl8139 (I suspect the defaults had got changed with out my notice). This was the culprit, as changing the NIC to virtio stabilised things and now it can run for long periods (still have occasional segmentation crashes). In addition I added a dedicated Seagate Skyhawk for the storage volume and this lowered system load compared with the LVM running on top of RAID1.
Hope this saves someone else aggravation.