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: 
For those coming here from a search - this is (currently) an old question with old answers, but there are other newer posts that answer this question better.

The solution I prefer is: 

`root# lsblk -io NAME,TYPE,SIZE,MOUNTPOINT,FSTYPE,MODEL`

```
NAME    TYPE    SIZE MOUNTPOINT FSTYPE            MODEL
sdb     disk    2.7T                              WDC WD30EZRX-00D
`-sdb1  part    2.7T            linux_raid_member 
  `-md0 raid1   2.7T /home      xfs               
sda     disk    1.8T                              ST2000DL003-9VT1
|-sda1  part  196.1M /boot      ext3              
|-sda2  part  980.5M [SWAP]     swap              
|-sda3  part    8.8G /          ext3            
|-sda4  part      1K                              
`-sda5  part    1.8T /samba     xfs               
sdc     disk    2.7T                              WDC WD30EZRX-00D
`-sdc1  part    2.7T            linux_raid_member 
  `-md0 raid1   2.7T /home      xfs               
sr0     rom    1024M                              CDRWDVD DH-48C2S

```

References:

* <https://unix.stackexchange.com/q/4561>
* <https://askubuntu.com/q/182446>
* <https://serverfault.com/a/5081/109417>
The sg\_\* utilities might also be useful:

```
$ sudo sg_map -i
/dev/sg0  /dev/sda  ATA       WDC WD5000BEVT-2  01.0
/dev/sg1  /dev/scd0  Optiarc   BD ROM BC-5500S   1.83
/dev/sg2  /dev/sdb  ATA       WDC WD5000BEVT-0  01.0
/dev/sg3  /dev/sdc  WD        PP III Studio II  0817

```

There are lots of other commands in the sg utilities such as sg\_scan, sg\_readcap and so on.

Also if you are booted from a redhat/centos cd you can switch to an alternate console and use the "list-harddrives" command to show disks attached to the system.