Considering a pair of 2000's

I also only use WAVs but refuse to use a hard drive with my players.  While flash drives aren't the most cost effective option, they have been far more reliable in my experience.  As long as you buy one that has fast read and write times you should have nothing to worry about.  I have a 64GB Transcend drive that I paid $108 for.  I use it with 2 CDJ-2000's in Link mode and have yet to have any problems.  I assume that the CDJ-2000 has a small internal buffer but I doubt is enough to make much of a difference if your hard drive spins down.  If you must have your whole collection with you (weddings, corporate events, etc.)  I'd suggest putting a playlist of tracks that you are certain you will play on a flash drive and connect a hard drive to the other CDJ's that contains everything else.

Thanks for the info Lossless. A high capacity SSD drive would be nice although it could be very expensive at the moment.

@Richie >  For a lot of the DJs on here, they find that a couple of large size flash drives are substantial for their needs at gigs (even when using .wav files - you can still store several thousand tracks).

However, if you do wish to use an external harddrive, then you shouldn't have problems. Analyse your files first in Rekordbox and then export to the drive for easier usability (categorisation / playlists / track data / waveforms etc). I do believe the CDJs continue to ping the drive to prevent it from going into 'hibernate' mode.

ssd is the best solution if you care about performance etc. I got 2 drives from intel, 80gb and 120gb, and i use them as external drives with usb3 cases and they rock. You don't need your entire music collection everytime you play...

To be honest the HD size issue was more for having my entire music sorted in rekordbox and stored on one medium. I'm sure 3-4 usb sticks would be more than enough. I like the idea of being able to browse thousands of tracks and being more selective.