Whenever you are dealing with an audio drive, be it recording or just playback, these three things are what should instantly pop into your head.
1. First and most importantly, USE FIREWIRE.
2. You want to make sure it has a spindle speed of at least 7200RPM with an 8MB or larger cache.
3. If you can, look for "Oxford 911" chipset.
LaCie Rugged All-Terrain Hard Drive 80GB $149.99
http://www.guitarcenter.com/shop/product/LaCie-Rugged-AllTerrain-Hard-Drive-80GB?full_sku=240429
Glyph netDrives USB + FireWire 400 Hard Drive 80GB $189.99
http://www.guitarcenter.com/shop/product/buy_glyph_netdrives_usb__firewire_400_hard_drive_80gb?full_sku=240291%2e556
Glyph netDrives USB + FireWire 400 Hard Drive 120GB $199.99
http://www.guitarcenter.com/shop/product/buy_glyph_netdrives_usb__firewire_400_hard_drive_120gb?full_sku=240292%2e715
Glyph netDrives USB + FireWire 400 Hard Drive 160MB $219.99
http://www.guitarcenter.com/shop/product/buy_glyph_netdrives_usb__firewire_400_hard_drive_160mb?full_sku=240293%2e558
Glyph netDrives USB + FireWire 400 Hard Drive 200GB $229.99
http://www.guitarcenter.com/shop/product/buy_glyph_netdrives_usb__firewire_400_hard_drive_200gb?full_sku=240294%2e200
Glyph netDrives USB + FireWire 400 Hard Drive 250GB $239.99
http://www.guitarcenter.com/shop/product/buy_glyph_netdrives_usb__firewire_400_hard_drive_250gb?full_sku=240295%2e560
Glyph GT 050Q Quad Interface Tabletop Hard Drive 250GB $249.99
http://www.guitarcenter.com/shop/product/Glyph-GT-050Q-250GB-Quad-Interface-Tabletop-Hard-Drive?full_sku=103833133
Glyph netDrives USB + FireWire 400 Hard Drive 400MB $499.99
http://www.guitarcenter.com/shop/product/buy_glyph_netdrives_usb__firewire_400_hard_drive_400mb?full_sku=240297%2e562
LaCie Two Big eSATA & USB External Hard Drive 500GB $399.99
http://www.guitarcenter.com/shop/product/LaCie-Two-Big-eSATA-USB-500-GB-External-Hard-Drive-?full_sku=241259
Glyph GT 050Q Quad Interface Tabletop Hard Drive 500GB $549.00
http://www.guitarcenter.com/shop/product/Glyph-GT-050Q-500GB-Quad-Interface-Tabletop-Hard-Drive?full_sku=104131123
Glyph netDrives USB + FireWire 400 Hard Drive 500GB $639.99
http://www.guitarcenter.com/shop/product/buy_glyph_netdrives_usb__firewire_400_hard_drive_500mb?full_sku=240298%2e721
LaCie Two Big eSATA & USB External Hard Drive 1 TB $499.99
http://www.guitarcenter.com/shop/product/LaCie-Two-Big-eSATA-USB-1-TB-External-Hard-Drive-?full_sku=241337
LaCie Two Big External Hard Drive with PCI-E Card 1TB $899.99
http://www.guitarcenter.com/shop/product/LaCie-Two-Big-1TB-External-Hard-Drive-with-PCIE-Card?full_sku=240159
Most computer based DJs have two portable hard drives & make an extra copy of their hard drive. That way if you have a problem with the hard drive you're using during a gig, you have a back up hard drive.
