drewp

Old disk

Current disk with ext3 (all units are powers of 1024, not 1000):

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       273G  251G  7.9G  97% /

debugfs stats says:

Filesystem features:      has_journal ext_attr filetype needs_recovery sparse_super large_file
Inode count:              36257792
Block count:              72505353
Reserved block count:     3625267
Free blocks:              5554423
Free inodes:              28537176
Inodes per group:         16384
Inode size:               128

I.e. there's an inode for about every 7.89 kB of disk. I suppose that was a ratio of 1 inode per 8kB. The inodes themselves are using 4.3GB. Then there's 246.7GB of file+dir data, which is an average of 1 inode per 34kB of stored data. 

New disk

When I run mkfs.ext4 on a new 2TB disk, the default filesystem is like this:

 
Filesystem      Size  Used Avail Use% Mounted on
/dev/sdb1       1.9T   28G  1.7T   2% /mnt

Filesystem features:      has_journal ext_attr resize_inode dir_index filetype extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize
Inode count:              121577472
Block count:              486281216
Reserved block count:     24314060
Free blocks:              478600693
Free inodes:              121577461
Inodes per group:         8192
Inode size:               256
 

The inodes are bigger, maybe for the subsecond timestamp precision (and higher-performance xattrs which I don't use), and apparently mkfs has picked 1 inode per 16kB. This leads to 28GB of overhead for inodes, which seems rough. Also it has arranged for a 92GB buffer space for superuser.

With these flags, I get a more sensible layout: mkfs.ext4 -v -i 32768 -m 1 /dev/sdb1

 
Filesystem      Size  Used Avail Use% Mounted on
/dev/sdb1       1.9T   14G  1.8T   1% /mnt

Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize
Inode count:              60788736
Block count:              486281216
Reserved block count:     4862812
Free blocks:              482399989
Free inodes:              60788725
Inodes per group:         4096
Inode size:               256