Linux: Why change inode size?

Tune2fs allows to change inode size from default (128 bytes on ext3, 256 bytes on ext4) to almost anything, but it should be power of two. What are the reasons for changing default inode size?

Here it's written that this can be done to be able to store ACL attributes inside inodes. What else can be stored inside an inodes?

Is there any reason to increase inode size on modern high-capacity drives (2TB and more)?

Solution 1:

I think by default current versions of mkfs.ext2/3/4 default to 256 byte inode size (see /etc/mke2fs.conf). This IIRC enables nanosecond timestamps with ext4, and as you say, more extended attributes fit within the inode. Such extended attributes are, for instance, ACL's, SELinux labels, some Samba specific labels.

Bigger inodes of course waste a little bit of space, and as you make them bigger you get into diminishing returns territory pretty quickly. The default 256 bytes is probably a perfectly good compromise for most situations.

Solution 2:

With the ext4 option inline_data (new in Linux 3.8), there is a new good reason for larger inode sizes: Given this option, the file contents can be stored in the inode of the file (if the file is small enough). This avoids one seek operation. I have not seen any real-world benchmarks for this, yet.