In a test-setup I put 561GByte of data onto a 1 TByte harddisk. The first disk is formated with ext3, the other with xfs.
Here are the results:
df -h
/dev/sdc1 932G 561G 372G 61% /media/disk1_1T
/dev/sdd1 917G 561G 311G 65% /media/disk2_1T
mount
/dev/sdc1 on /media/disk1_1T type xfs (rw)
/dev/sdd1 on /media/disk2_1T type ext4 (rw)
Ok, by default ext reserves 5% for root-only usage, after removing that reservation ext4 ist still behind xfs:
tune2fs -m0 /dev/sdd1
Setting reserved blocks percentage to 0% (0 blocks)
df
/dev/sdc1 932G 561G 372G 61% /media/hd51_1T
/dev/sdd1 917G 561G 357G 62% /media/hd53_1T
Conclusion: ext3 reserves 15GByte more administrative space.
Of course, it’s not all about efficiency.