Formatted vs unformatted size of filesystems on linux: ext3, ext4, xfs, zfs and reiserfs

A small comparison of formatted space differences between ext3, ext4, xfs, zfs, btrfs, ntfs and reiserfs.

Every one of us has beliefs. One of mine was that if I finally have the time and courage to start using ZFS on linux1 compression and encryption will be some much easier and I’ll have so much more space on my disk.

As most beliefs, this proven to be wrong.

First of all, ZFS on linux does not support encryption, so I needed to add a LUKS layer. After that I turned on lz4 compression and let my copy go for the night. I have a few things and copying 845GB takes a while.

The reason I thought I can gain a little space is that I have all kind of data on that disk; what I was unaware of if that how little the compressable data is out of the all. JPEG is compressed, RAW images are compressed, flac, mp3, mp4, xvid - all compressed. So in reality, on your media drive, you won’t get any good of the lz4 compression - alltogether I only gained 10GB and I suffered a significant performance loss. If I’d have RAID and I was on BSD, where encryption is an actual option, I would have stayed with ZFS, but for this purpose it did not suite me at all.

After this brief experience, since my data could be formatted again, I tried out a few different filesystems. On ext3 and ext4 I even added the -m 1 magic, to reduce the reserved space to 1% and the results are the following:

Size Size -h Used Used -h Free Free -h
unformatted 999664124 999.7G
ext3 960783720 917G 73496 72M 911898500 870G
ext3 tune2fs -m 1 960783720 917G 73496 72M 950947880 907G
ext4 960783720 917G 73364 72M 911882248 870G
ext4 tune2fs -m 1 960783720 917G 73364 72M 950931628 907G
xfs 975757820 931G 34208 34M 975723612 931G
zfs 957874048 914G 128 0 957873920 914G
reiserfs 976204696 931G 32840 33M 976171856 931G
ntfs 976234492 932G 95780 94M 976138712 931G
btrfs 976234496 932G 16896 17M 974107392 929G

The winner is ReiserFS - but it’s old and abandoned and there is a bit of a moral issue with it.

The next is XFS, which would have been my choice - but it does not support file creation time2, which, for historical reasons, I want to have. My filed used to be on NTFS before my linux times, so I do actually have creation dates as I migrated the data to ext4 from there, also storing creation dates.

NTFS is a brilliant filesystem, a full-fledged beast - sadly not designed for linux and to get POSIX permissions on them is a bit too tricky.

Therefore I decided to go with the new kid on the block: btrfs. I was finally titled stable a while ago and it gives me 22 more GB to play with, and it has a semi-intelligent compression option which, in theory, will skip compressing already heavily compressed data, which is good for performance. I do have a bad feeling about it, but my data is backed up on more mature filesystems as well.


  1. http://zfsonlinux.org/

  2. https://en.wikipedia.org/wiki/Comparison_of_file_systems



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