Question: So I have a server that has a few harddrives in it, all formatted and mounted. However I'm told there is another drive attached to it. How do I find out what drives are attached? How do I find out the device filename for this new drive (that's not mounted)

Answer: 
`fdisk -l`​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​
Depends on how the drive is attached.

ATA/SATA drives should normally be detected on bootup. Look into the boot log (`/var/log/syslog, /var/log/messages`, output of `dmesg`).

There should also be a list of recognized partitions for all partitioned drives under `/proc/partitions`.

For hotplugged drives (e.g. USB) it depends on how the distribution manages them. Usually modern distros use udev (older might use hotplug or hald). The log is configurable, either a separate log under `/var/log`, or in the general log `messages` or `syslog`).