External hard drive causing Midi playback issues

[ProtocolDroid]

Hi, I am new to both this forum and everything Mac so I would be grateful for some help.

I recently bought a new iMac (3.5 ghz quad core i7, 16gb ram) which I run logic on. I have a Zoom R8 as an audio interface, a Yamaha mox8 as a midi keyboard and external sound source plus a G-tech 2tb external hard drive for recording audio onto.

 

I have recorded a track using one of the mox8 piano sounds. Sometimes, during playback, the sustain pedal information recorded in logic 'drops out' resulting in a choppy piano part. I have noticed that this happens when the external drive's light is flashing and, presumably, the drive is active. I originally connected the drive using USB 3 and have now tried a thunderbolt to FireWire connection but, I get this occasional playback issue. Eventually, I will need to convert the midi to audio so that I can mix the track properly but I am frustrated that it may require a few 'takes' if the sustain information is interrupted randomly.

 

I hope this makes sense and I would be keen to know if anyone has any theories and, hopefully, solutions to this problem.

 

Thanks.