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Persistent Disk Cache is like a 'permanent' / stable copy of your RAM previews.
It may be persistent in that even data garbage (=invalidated cahce files from crashed projects etc.) is sticky like chewing gum on your shoes, but I'm not too sure about "stable" or reliable. Some plug-ins like TrapcoParticular still struggle with this cache stuff even today... Also AE's caches are not necessarily a reflection of the RAM previews. Just like the conventional RAM caching they work on a per-layer/ per(pre)comp basis. The very specifics of how much data is actually pulled from the cache depend on the project and often enough you will see the program re-caching because something has changed.
- Hypothetical. Whether it's practical or not, would performance increase by having PDC and Media Cache on separate drives?
- Practical. In actual practice, if PDC is placed on the same drive as the other Caches/Scratchdisks, will this create noticeable slowdown/issues?
To quote from a Ferengi in an episode of one of the Star Trek TV series: "I don't know how to speak hypothetically." That is to say you won't know until you build the actual setup and start working. Of course separate drives are always better not just for speed but also data security/ safety, but the actual throughput will be determined by how you work and what makes up your project. With just a handful of simple graphics files you will never know the difference even on a slow system, but if you work with lots of 4k clips you could exhaust bandwidth on a fast system. You could be plugging all your devices to the same SATA buses and that might translate down to being on the same PCI bus and then none of this really makes a difference because you already get collisions on the PCI protocol level, if you get my meaning. So for better or worse, unless you have made up your mind about actual components it will and shall forever remain a very theoretical, abstract and academic debate. All the whitepapers in the world can be useless, if your workflow doesn't fit in one of the proposed standard models and example references...
OK. I understand. =)
Then let me try this: for starting out with After Effects and primarily using it to embellish and spruce up 1080p lossless/uncompressed footage, if my current design has a separate SSD assigned for Media Cache/Scratchdisks, would it be "okay" to just point the Persistent Disk Cache to the same SSD? Or should I buy another SSD and set it aside for the PDC?
I know no answer can be perfect, but an experienced user's wild guess is going to outperform my best guess right now due to the differences in practical experience. =)
Yes, it is OK to use the same SSD for both kinds of cache. If you had lots of extra money, you could get some small speedup by separating them, but it's not crucial to do so.
Hey! I know you! You're from the video guides and help files! You're like the GLaDOS of After Effects, except not evil.
I think that's about the most definitive response I could have dreamed of. Thank you for taking the time to answer my little question. =)