How to set up HDs for optimal performance?

Hey guys,

I'm new to this forum so I hope I am posting in the right area. 

I've run into a huge problem this week and haven't been able to come to a solution. I have 3 HDs: one iMac 2011 internal HD (1TB), one OWC Mercury Elite Pro (2TB) and one Mercury Elite-AL Pro (2TB). According to many posts that I have read online for optimal performance you should keep one drive dedicated to all your LPX projects and samples which is why I save all of those to my Mercury Elite Pro. I just recently started working on a mix with over 100 tracks (all audio). The project will load up quickly but when trying to make the simplest edits, I get the crazy spinning beach ball for 2 seconds and finally it will play but when I press pause the playhead will continue playing about a second before actually stopping. It's making it almost impossible to work. 

I don't think it is a RAM issue because: 

- I have 20GB RAM 

- I never get the System overload message

- I've changed buffering to different sizes (128-1024) 

- I've toggled through cores but typically leave it on automatic

- And most of all in the CPU meter the CPU looks fine but the HD meter is freaking out every time I press play. 

This is why I am thinking it is an HD issue. Both external drives have 7200rpm with 800FW so I don't think they should be that slow. Other projects seem to be fine even when recording and I believe the most tracks I've worked with in the past have been about 70 tracks (both audio and midi, including effect plugins) but never had this problem.

Do you guys have any suggestions? An SSD is a little much for my budget at the moment.

This happens as soon as I click play. But it doesn't start playing for about 2 seconds.

Use at a program to look at fragmentation of audio file drive..  You should leave at least 25% free..  If the drive gets too full or fragmented, computer must scatter one audio file in several places. If a lot of files are fragmented, it becomes a lot of work to assemble each of the 100 audio files. If you make an edit, it's a lot of work to move around all tracks. 

I would defrag a drive. then 'save a copy' of song project to a drive with a lot of open space. . so all the audio files are NOT fragmented.  You might have also reached the maximum number of audio tracks you can play with a FW drive..  A SSD would fix that.

An alternative is to submix some tracks to a stereo pair. (save original if you want to make changes).. So you are only playing 70 stereo tracks.. 

I used to submix all audio tracks ( I sometimes build up a huge amount of audio tracks).  Then I open a new project and import stereo mix, to do substantial vocal overdubs.. I mix the vocals down, and import back into original. 

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