What does this mkfs.ext4 operand mean?

Question

I am using GParted (0.28.1, Fedora 25) to format a external drive and noticed that the command displayed is:

mkfs.ext4 -F -O ^64bit -L "INSTALL" /dev/sdd1

When making disks in the past from command line I have just used mkfs.ext4 DEVICE which seemed to work well for various architectures. However the above includes the option -O ^64bit, which I guess removes some default 64bit feature of the filesystem so it works with 32bit. Does it do this and is normally necessary to pass it on modern Linux OSs (to enable compatibility with 32bit etc systems), and what cost could it have other than probably reducing the volume size limit?

Solution 1

The default options for mke2fs including those for ext4 can be found in /etc/mke2fs.conf. They could be different depending on the distro you're using. I'd take a look at that file on any distro you're curious about to see if the -O ^64bit param would be necessary. According to the man page the '^' is indeed the prefix used to disable a feature. The effect of not using 64bit ext4 is that you'll be limited to ~ 15T volumes. Where as you can have 1EiB volumes if you use the 64Bit flag. HOWEVER, 16T is the recommended max volume size for ext4 anyway.

Solution 2

The reason the option -O ^64bit was added (under some circumstances) to the mkfs.ext4 command line is that the Ext4 64-bit mode caused problems with boot loaders. You can read all about it in this gparted bug report.

Comments

[TheBeginner]

Even with work rendering files I think I would be more worried about hitting that limit with modern games xD