I've heard several horror stories regarding EW's Play engine, but they all seem to be related to Play 4. 
 
So for the foreseeable future, I intend to stay with Play 3.

I also use LA scoring strings on an SSD and it works flawlessly, loads fast.

Jonesey hit the nail on the head above... the head stack assembly (HSA) in a magnetic HDD is a rigid set of "fingers" which has the head gimbal assemblies (HGAs) on the tips... so even partitioned, the drive can only read/write one file at a time. The O/S drive gets the most use and need to access files quickly, so "data" on that same drive causes competition on files.
 
Two physical drives will allow your system to multi-task more efficiently, especially separating O/S (and programs) from data. An SSD has the advantage of no moving parts, so these are ideal as the O/S drive (i.e. when primarily reading files). I have seen mine get flaky when stressed with read/write operations, so I have defaulted to SSD for O/S and programs, and HDD for data storage.
 
Also, SATA III for all drives is important... I have seen a few folks buy SATA II SSDs and disappointed with speed (a SATA II SSD is a waste of money IMO).

Also worth noting that read times are faster on the outside of the disk and get slower as you move toward the center. So make sure you have your samples on the first partition (I believe the partition diagram from left to right generally means outside to inside). I read somewhere that read speeds are halved on the inner side of a 1TB drive. Of course this doesn't apply to SSD's.

I used to have problems with Hollywood Strings, but putting the library on its own SSD resulted in major improvements.
 
As for Play 4, it acted wacky with Sonar on my system, so I went back to Play 3.

You shouldn't need to defrag a drive that is only being read. The files aren't actually being moved around and as they were copied to that drive in one go should already be in contiguous chunks.

SSD drives are the way the go, if you've got the bucks. They are fast, fast, fast.
 
Scott

--
Scott R. Garrigus - http://garrigus.com - SONAR X2 Power! - http://garrigus.com/?SonarX2Power
* Author of the Cakewalk Sonar and Sony Sound Forge Power book series: http://garrigus.com/?PowerBooks
* Author of the Cakewalk Sonar ProAudioTutor video tutorial series: http://garrigus.com/?ProAudioTutor
* Publisher of the DigiFreq free music technology newsletter: http://digifreq.com/?DigiFreq
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OK, guys.  I will get an SSD for Hollywood and Vienna.  Sounds good.
 
By the way, I have been WAY happier with Vienna's engine than with Play, although with some of the smaller librarie (like Fab Four) Play seems to be fine.
 
I appreciate everyone's comments here.  And I would be glad to hear any Vienna or Hollywood masterpieces you have created.