The system Lincoln described IMO is the way to go for.
I'd keep each and every program on the system drive (most of them won't be happy to be placed anywhere else but in their default locations anyway, especially true for Apples own applications) and put all samples, projects and whatever "user data" somewhere else.
But then, hold on!
This procedure can only be considered "universally true" for Mac Pros, which offer several options of access to fast additional HDDs:
- Internal SATA conncetions.
- PCI cards for eSATA drives.
- PCI cards for more FW ports to connect drives to.
None of these exist on an iMac, you only have one FW port and 4 x USB.
Neither of those will give you a remotely similar performance than what you're getting from your internal drive, so it might as well be clever to run everything from the internal drive until you actually run into its limitiations. After that, I'd start with putting project/audio data onto an external drive - usually, even for advanced audio projects, the disk demands are comparatively low (at least compared to the demands of modern streaming sample libraries), so one should be able to run all audio data from a decent external USB drive.
Another idea would be to consider Optibay, they're offering replacement kits for the DVD/CD drive, so you actually get a fast second internal drive (the Superdrive can be kept in an external USB chassis). IMO this is the best option for anyone not owning a Mac Pro or MBP 17" (which at least has an Expresscard slot).
Otherwise, as long as you're not actually running into disk performance problems, I'd recommend keeping things on the internal drive. Just make sure to regularly back up everything as the system drive could wear out...
As a tip: I'd partition the system drive into two (or maybe 3) partitions for organisational reasons.
1) System only. This can be backed up quickly, using Time Machine, SuperDuper, CCCloner, etc. Really, system backups go a LOT faster if you don't have any other data on a partition.
2) All other data.
Or, as said, alternatively:
2) All sample libraries. You have them on DVDs (or backups) anyway, so this is a partition that doesn't need any regular backup schedule (the worst that could happen is that you'd have to copy things from DVD again...).
3) All your "user created data", such as Logic projects, documents, photos, etc. Again, this is for easy backup purposes.
If you don't have problems with backing up the entire shebang, should you keep it in one partition, don't bother. Personally, I prefer a complete system backup which is done in half an hour (which I do around once a month, depending on how much I installed). And I backup all important projects each evening, anyway.
Really, just a convenience thing, nothing to do with performance.
- Sascha
