"Couldn't find valid filesystem superblock" while adjusting ext4 filesystem with tune2fs

I've a shiny new Ubuntu 11.04 installation. In addition to the system disk, I've added a 2TB drive (/dev/sda) for data.

System monitor reports 1419.5 GiB "Free" and 1326.3 "Available".

Reading around the web leads me to believe that the system is reserving this ~6% as "root reserved space"

Well, I don't think I want "root reserved space" on a pure data disk, so I tried the oft suggested:

tune2fs -m 0 /dev/sda

on the drive only to receive:

tune2fs 1.41.14 (22-Dec-2010)
tune2fs: Bad magic number in super-block while trying to open /dev/sda
Couldn't find valid filesystem superblock

The filesystem is ext4 and the partitioning is somehow "GUID" (<- Not familiar with this one)

The mighty Google was little help. Can anyone out there tell me how to eliminate the "reserved space" on this new data drive?

Thanks.

1 Answer

You should be accessing /dev/sda1, not /dev/sda.

/dev/sda is the entire disk. Partitions on the disk are assigned numbers, e.g. /dev/sda1. With limited exceptions (e.g. SD cards), individual partitions, not entire disks, are formatted with filesystems.

If the filesystem is somehow on the whole disk, you'll want to repartition the disk using fdisk or a similar utility so that there's at least one partition. You can then format /dev/sda1 as ext4. This operation will erase all data on the disk, so be sure to back up anything important before you proceed.

For NVMe SSDs, you'll typically use /dev/nvme0n1 for the disk (NVMe device 0, namespace 1¹), and partitions are designated p1, p2, etc., as in /dev/nvme0n1p1. If you have more than one NVMe SSD, the additional disks will probably be named /dev/nvme1n1, /dev/nvme2n1, and so on, with the same p1/p2/etc. suffixes for partitions.

¹NVMe allows devices to have multiple namespaces. These allow a single drive to be treated as multiple devices, even though they may physically use the same connection. Multiple namespaces are almost never seen outside of enterprise/datacenter SSDs, so you should never need to deal with devices like /dev/nvme2n3p1 (device 2, namespace 3, partition 1).