FAQ/Cache to disk

From VFXPedia

Using the cache to disk option in a large comp can dramatically increase performance of a project inside Fusion. What the cache is actually doing is rendering every tool upstream of the cached tool, and saving the selected cache to disk.

The following is a collection of tips and issues with Cache to Disk.

1. DFX+ 5 does not support disk caches, so do not try using them in this version of the program. Only Fusion supports disk caches.
2. Don't cache every tool in the comp, just key tools that have upstream branches that need a speed boost. Generally you will want to cache anything that is processor intensive (glows, blurs, etc.) or very large branches of a comp.
3. If you are finished in that branch, you can choose to lock the tools upstream from the cached tool. Otherwise, any change to an upstream tool will invalidate and clear out some or all of the disk cache.
4. You do not have to pre-render to place a disk cache on a tool. You can enable a disk cache and not render. As each frame is processed it will be placed in the cache, at the quality and proxy level of your current interactive frame (unless a cache already exists of that frame at a higher quality).
5. Network rendering of disk caches is possible. All paths need to be accessible to all slaves involved, including the DiskCaches: directory (in the Path Map preferences page), which is where the cache files will be written, and the Previews: directory, used by slaves to load the comp file. See the Network Rendering FAQ for more details.
6. There is an issue in Fusion 5 and previous versions, where sending off more than one network cache at a time will not work 100%. Currently, all cache to disk over the network uses the same comp name, and if sending off more than one, there is a possibility of overwriting the next queued comp. So you may end up missing a cache even though you have sent it to network render. To avoid this, just be sure to let the first network cache finish before you send off the second one.
7. If your cache is empty at a given time, and you are in proxy mode, you will get a proxy frame saved into your cache. If you want Fusion to produce a full quality frame while working interactively, you have to check HiQ, and disable proxy. Fusion can only save what it renders. If you pre-render your cache, you can produce a full range of final render quality frames for your cache.
8. If the cache at time x already has a frame stored in the cache it will only replace that frame if the new frame is of a higher quality than the existing cached frame. In other words, a full resolution HiQ frame in the cache will not be replaced by a proxy frame, but a proxy frame will be replaced by a full resolution frame.
9. Don't enable Lock Cache, unless you know what you're doing. Locking the cache can result in subtle or major differences between the upstream tool settings and the results from the cache. If you must do this, we recommend Lock Branch too, otherwise it will drive you nuts, as the cache and the upstream tools can be different and out of sync. Just not a good idea.
10. Always leave RAW files enabled when you create a disk cache. Only the default .raw format files contain the necessary info to handle proxy sizing correctly - anything else, and not only will you likely get proxied frame issues, but you'll get HiQ/non-HiQ problems, you'll lose any extra channels or 16 bit depth info, maybe field problems, etc etc.