what is the best way: when level is loading put all static vertices into vbo directly and draw them using index vbo, or once load them into memory, then put them if needed to vbo, unload them if they are not needed? I think if level is big, all object cannot be loaded in video memory. Is vertices are in vbo, can render make frustum culling or other algorithm? If you know how can data be organized efficiently, tell me;

You should not make a VBO too large. Something like 4MB is ok so that the driver can easily do memory management. If your map is really huge and consumes 100 VBO chunks, each 4MB = total 400 MB
then the driver will do its memory management as usual (it always keeps a backup copy in RAM).

Thank you, but I cannot understand, should I put all data, including models, into vbo or not? 4Mb is about 1 000 000 vertices (without normals, texcoords) are not too large for thing in fact. 400 Mb? but if video memory is 256 Mb only? More important, will be work octree, if data is on video memory? Maybe my questions seem simple, but I am beginner with vbo