Now for the configuration issues - multiple drives, where to put the swap, etc.
We can split disc access into three major chunks: loading/swapping application code, accessing application data, and general data swapping.
Application code undergoes swapping, just as data code does. Your application can be loaded into memory, but if a chunk of the application code goes a long time without being run, it gets swapped out. Application code is always swapped out to the place it came from on the drive, and takes up no space in the pagefile. However, when it needs to be swapped back in, you see a performance hit similar to the first time you run the application, since the code must once again be loaded from disk.
Your application data is relatively self-explanatory - this would include your actual DWG file, and the temp files Autocad creates, etc. This data is read from disk, or written to disk, in direct response to user operations.
Then there is data swapping. This is the "behind-the-scenes" action, where Windows automatically moves data to/from RAM and the pagefile, in order to make sure that operations that are currently running have enough RAM.
To get absolute best performance, each of these three categories of action would hit a separate drive. This is where we start to see Michael's recommendation of putting the swap on its own drive. If it's on the primary drive, then application loading/swapping and data swapping will hit the same drive, possibly at the same time, causing the disk drive to rapidly jump back and forth between disparate locations on the disk. This is what we want to avoid. If we are also storing all our DWG files and temp files on this same drive, we see an even bigger hit in performance, as all these operations may end up in a fight for simultaneous access to the drive.
Now, in an office situation, many people have their DWG files on the server. This off-loads one item, leading to a potential increase in performance (unless you have a slow network). So now we're looking at the application loading/swapping, and the pagefile access.
Now, if we want to use only two drives, what is the best way to handle this?
Method one is to use one drive for the primary, the other for swap. This means that the majority of the swap drive will be unused, because our swap file is probably less than 4GB in size. But it can be used as a generic storage drive. This now gets our swap space hitting one drive, while the other is reserved for application loading/swapping, and temp files. This is an ideal situation for someone with not-very-much memory, such as 1GB of RAM, where swapping happens pretty much continuously. But if you have 4GB of RAM, the benefits are much less, because your system doesn't need to swap any where near as much.
So now let's compare that to a RAID 0. With the RAID 0, we are now hitting the same drive for application loading/swapping, temp file usage, and swap space. But if we have a lot of RAM, we won't notice much of a difference having the swap space hit the same drive as everything else, because our computer won't swap much. However, we'll notice a HUGE difference in application loading/swapping and temp file usage, because of the RAID 0, which typically results in about a 30% gain in overall disk performance over a single drive.
This is why I say you will get far more bang for the buck using two drives in a RAID 0, as opposed to dedicating one as a swap drive. If you want to throw a third drive in there, then by all means, set up the first two drives in a RAID 0, then use the third drive for swap and overflow data storage or backup. But in general, you will notice an overall increase in EVERYTHING if your primary drive is a RAID 0.
The big rule in all this is NEVER NEVER NEVER use a removable (i.e., external) drive for swap space. If that connection gets interrupted, or you try to startup your system while the drive is powered down or disconnected, bad things will happen.
Now for the point Numa brought up: which RAID? First off, RAID arrays should NEVER be used for redundancy or recovery. That's what backups are for. A RAID 1 is useless, except for in very limited situations, typically only for servers that should not fail unexpectedly. In other words, if that server MUST remain up as much as possible, you may want to use a RAID 1 or RAID 10 or RAID 5. Those systems are designed so that the system can keep running (for a time) after a disk fails. However, it is designed only for short-term redundancy, basically, only long enough until the IT person can get there, shut down the server in an "official" way, and replace the failed drive. But rebuilding ANY sort of RAID array is more trouble than any sane person would want to deal with, so it should not be considered a path to data redundancy/recovery. Use a good backup system instead. And when you stop looking toward RAID as something that provides redundancy or backup, then a RAID 5 (or even a RAID 10) is obviously not worth the expense.
As far as a RAID 0 being more trouble than it's worth, I strongly disagree with that. The argument against using a RAID 0 is basically that, with two drives involved, the chance of a drive failure is twice as great as when only one drive is involved. However, these days, disks are good enough that drive failures happen very rarely. I don't view this as a big concern. Once upon a time, it was a valid concern, but not any longer (in my opinion). If one of your drives fails, then you just deal with it the way you would deal with it if you had only the usual single-drive system, and your single drive fails.
Personally, I really like having 20-second startup times for Civil-3D. Not to mention, software updates and installations go at blinding speed. And that doesn't happen unless you have a fast primary drive, namely multiple fast drives in a RAID 0.
