If a firewire drive doesn't mount or comes up as "eject or initialize". HIT EJECT!!

Try to run disk warrior to see if that can fix the problem.
1. unhook the drive
2. start diskwarrior
3. plug the drive in (the message is now suppressed and the drive shows up in the list)
4. select it from the list and hit rebuild

The FW bus can only run as fast as the slowest device on it. Although Macs, PCs, and most drives should be talking S400 (400 Mbit/sec), many cameras and decks, both consumer and pro, only support S100 or S200 speeds. If you hang an S100 deck on your bus, you've just cut max throughput by a factor of four...
more on Adam J. Wilt's website

If playback is stalling, try disconnecting some, or all, of your Firewire drives. Although the Firewire spec allows up to 63 devices to be connected to your computer, after about five or six drives, there's so much "talking" on the Firewire bus that performance really starts to degrade. Where possible, limit the number of Firewire drives you are using. Worst case, buy bigger drivers and copy data from smaller drives to bigger drives so you total storage remains the same, but the number of devices decreases.

Good firewire rules:

• Don't mess with the connections if the drives are active and always trash the drive icon before unplugging
  respect that "undo what you did" message if you do something to the connections
  I've lost drives by ignoring it and restarting.
  
• If the "Eject or initialize" message comes up and you go for initialize, make sure to choose "Mac OS Extended"
  (it comes upwith standard by default)
  or you will get weird behaviour of drive not showing enough free space and computer crashing.
  
• Don't use firewire drives as a storage or backup drive. one crash or instable situation can erase all the data.
  
• Use DVD-ram or CD instead for backups.
• IDE drives and SCSI drives are much more reliable in a high stress deathline environment.