Hi, I'm retiring my overworked laptop for a ground-up dedicated DAW build.  My question is should I use 2 drives or 3 if I am using SSDs.  
 
Using 2 drives:
C (SSD 500 GB): OS, Cakewalk Program, VST folder, Content folder, Command Center
D (HDD 1TB): Projects
 
If I were to use 3 it would look like:
C (SSD 240 GB): OS and Cakewalk Program
D (SSD 240 GB): VST folder, Content folder, Command Center
E (HDD 1TB): Projects
 
My thinking is that during recording, the application, VSTs and Projects are most active.  I know that the seek speed of SSDs are much faster than HDDs suggesting that 1 drive for everything except Projects might be enough.  Are there other significant factors like throughput (too much info in the pipe)  Would a 2nd SSD allow better throughput into the board?  (Please forgive my lack of accurate language.)
 
Thanks
 

If you're using sample libraries, you want at least three drives.

• OS/Apps/Plugins (not accompanying sample libraries)
• Audio/Projects
• Samples

silver son
 
If I were to use 3 it would look like:
C (SSD 240 GB): OS and Cakewalk Program
D (SSD 240 GB): VST folder, Content folder, Command Center
E (HDD 1TB): Projects
 Would a 2nd SSD allow better throughput into the board?  (Please forgive my lack of accurate language.)

Not for this config. I have all of X2, X3 and Platinum (multiple versions), all the Rapture free and paid expansion packs, a few DPro packs and hundreds of plug-ins installed on my system 240GB SSD with plenty of room to spare. From a performance perspective, there is no reason to break out VST binaries and Cakewalk Content to another disk. I did put the Command Center cache on my project drive using a directory junction though to have a large area for quick access to old installers.
 
As Jim mentions if you use other sample-based software, in my case Superior Drums and  BFD, those samples are on a third drive. I do not use Kontakt or any of the other major sample-based synths but they would have their libraries on drives other than the system or project drives too.

Jim Roseberry
If you're using sample libraries, you want at least three drives.

• OS/Apps/Plugins (not accompanying sample libraries)
• Audio/Projects
• Samples

This ... and get the regular backup of each one in place right from the start ...

 I have 4 total.  I still don't get why people think it's convenient to put VSTs on a separate drive.  Most of them are small unless they are romplers.

I plan on adding a 4th drive, a 1TB SSD, for sample libraries when I can afford it. 1TB SSDs are still kinda pricey, but will no doubt keep coming down.
 
I remember the first time I saw a 1 GB disk drive. It was the size of a dishwasher and cost $50,000. Incredibly, they actually trusted me to take them apart and put them back together again. Some years later I bought my own 1 GB drive for $180. Now I've got the equivalent of 2,500 of those in my current computer. 
 
Anybody keeping track of 1TB SSD prices?

bitflipper
I plan on adding a 4th drive, a 1TB SSD, for sample libraries when I can afford it. 1TB SSDs are still kinda pricey, but will no doubt keep coming down.
 
I remember the first time I saw a 1 GB disk drive. It was the size of a dishwasher and cost $50,000. Incredibly, they actually trusted me to take them apart and put them back together again. Some years later I bought my own 1 GB drive for $180. Now I've got the equivalent of 2,500 of those in my current computer. 
 
Anybody keeping track of 1TB SSD prices?

All of the time.  Way too much for me. Meanwhile I also keep track of HHDs.  I've seen 1GB WD Blacks under $80. I see some WB Blues 2TB for under $80. I may have to upgrade a 1TB to 2TB. My drives could be featured on an episode of Hoarders.
 
 If I had a board with 12 SATA ports I'd be buying those 500GB SSDs.

bitflipper
I plan on adding a 4th drive, a 1TB SSD, for sample libraries when I can afford it....
Anybody keeping track of 1TB SSD prices?

I used to, when I had the same plan.  Then I decided on a different tack.
 
I bought a smaller, more affordable SSD (256GB), and only put my most-used sample libs on it.  I have way too many total to try and house on one SSD.  But I use maybe 12 or so regularly.  So those "faves" are kept on the SSD and the rest on a 4TB HDD.
 
Works a treat.  Of course, it doesn't shorten all load times, but maybe 80% for me.

I have the following setup:

1. SSD 120GB: OS, Apps, VSTs
2. SSD 120GB: Multisamples + libraries (e.g. drum maps, templates)
3. SSD 120GB: Current & recent projects

Plus other non-SSD drives (some partitioned) for storing the following:

• Older projects
• Exports & mixes
• Misc music-related stuff
• Manuals & reference material
• Software installation files
• CCC downloads
• Visual media
• Backups

Obviously some users need a much bigger drive for multisamples than I do.