Is it possible to add a disk drive to a RPi

It's difficult to do a permanent mount of what is essentially a removeable, hot-pluggable, device. You can try the following though

# blkid

/dev/sda1: UUID="898ee85d-ee12-4ab1-af0b-dece508ba70a" TYPE="jfs"

then edit /etc/fstab and add a line like the following

/dev/disk/by-uuid/898ee85d-ee12-4ab1-af0b-dece508ba70a    /data     jfs     defaults     0     1

where /data is the mountpoint and needs to exist as an empty directory. Make sure the file ends with a blank line.

Whether this is automatically mounted for you on boot depends somewhat on whether the disk has spun up and the usb subsystem has detected it before the boot sequence has tried to mount devices from fstab.  If it doesn't mount automatically, you can simply type 'mount /data' later to mount it.

If you reformat, repartition, change the filesystem type, then it's a good bet that the uuid will be re-written and you'll need to update the line in fstab.

I've never had to do the UUID that Selsinork is suggesting and my Pi does the mount at boot just fine of a usb drive.

Quick questions:

    Are you trying to power this drive through the Pi's USB ports? 

    You say latest version of Debian, but is that actually Raspbian?  I ask because they seem to call debian the soft-float version and Rasbpian the hard float version (the hard float version makes use of a built in device on the SoC to get better performance)

    What is the file format of the drive

The ultimate answer is to look into fstab.  Even if it's seeing the drive, it won't mount it unless you tell it to make it accesible in a specific location as Selsinork said. 

The UUID piece is mainly so that, in theory, you always get the same device mounted in the same place regardless of device detection order. If you use /dev/sda1 and inadvertently leave a usb memory key attached then there's a chance that the key gets detected first, is assigned /dev/sda1 and gets mounted instead of the drive you expected.

If you only ever connect this one drive, you're safe using /dev/sda1, but the nature of hot-pluggable busses means that's unlikely. Especially when USB is effectively the only expansion bus on the board.

I'm not a fan of the disk-by-id & disk-by-uuid methods as they rely on data that's not guaranteed to be unique (clone your disk using dd and the clone has the same uuid since it's written to the disk) however they're no worse than many other methods.

In a lot of ways I prefer LVM where you can use /dev/mapper/volumename, but LVM is overkill for a single volume on a single disk.

The other way would be to use nfs and mount some filesystem exported from elsewhere on the network, however my relatively untouched Raspbian image doesn't seem to mount nfs from fstab by default.

Even if it's seeing the drive, it won't mount it unless you tell it to make it accesible in a specific location as Selsinork said. 

The exception to that is that often when you boot to a desktop environment they tend to run some process in the background that checks for new storage devices, mounts them under /media, and then pops up an icon on the desktop.

selsinork wrote:

 

The UUID piece is mainly so that, in theory, you always get the same device mounted in the same place regardless of device detection order. If you use /dev/sda1 and inadvertently leave a usb memory key attached then there's a chance that the key gets detected first, is assigned /dev/sda1 and gets mounted instead of the drive you expected.

If you only ever connect this one drive, you're safe using /dev/sda1, but the nature of hot-pluggable busses means that's unlikely. Especially when USB is effectively the only expansion bus on the board.

Very true, I've only worried about a single USB device on the Pi so I haven't had to worry about things like that.

selsinork wrote:

 

Even if it's seeing the drive, it won't mount it unless you tell it to make it accesible in a specific location as Selsinork said. 

The exception to that is that often when you boot to a desktop environment they tend to run some process in the background that checks for new storage devices, mounts them under /media, and then pops up an icon on the desktop.

Right again, I don't really like going into the gui on the pi so I didn't think about it, lol

I run Openelec on my RPi all the time and mount USB drives no problem as long as I do it on a powered hub...