====== BTRFS vs ZFS ======

My target is to:
  * protect private files (Photos, documents) (of course I have scheduled backups to external device). On ZFS I can create subvolume with copies=2. On BTRFS with single disc it is not possible.

  * reduce e-mail disc space usage (compression, deduplication). On both I can enable compression with similar results. Deduplication works better on BTRFS, because I can specify small block size 4kB. Also is performed by external tool and it is not consuming RAM all the time, like dedup tables in ZFS.

  * deduplicate mp3 files grouped in folders

With single disc setup, there is no big difference between features provided by both filesystems.

Things to consider:
  * BTRFS is integrated by default, ZFS-fuse is old, ZFS native is provided as DKMS but can cause problem if kernel will be upgraded
  * BTRFS lacks of data redundancy (ZFS copies=2), but I can live without it because I have external backup.
  * BTRFS deduplication looks better (no constant RAM consumption)
  * ZFS offers better tooling 
  * BTRFS support attributes (like +c = compress)
  * user quota ???

 
===== Features =====

^ Feature                       ^ ZFS    ^ BTRFS  ^ remarks ^
^ License                       | CDDL   | GPL    |  |
^ Copy-on-write                 | Yes    | Yes    |  |
^ Checksums                     | Yes    | Yes    | ZFS: 256bit fletcher2 or SHA256; BTRFS: CRC32c|
^ Encryption                    | No     | No     | workaround with encryption of underlying devices |
^ Online defragmentation        |        | Yes    |  |
^ Online growing / shrinking    |        | Yes    |  |
^ Online block dev add/rem      | Yes(-) | Yes    | ZFS: only mirrored devices can be removed |
^ Online deduplication          | block  | No     | btrfs: planned, external tool available |
^ Online compression            | Yes    | LZO / ZLIB | similar compression level |
^ Subvolumes                    | Yes    | Yes    |  |
^ Subvolumes inside subvol.     | Yes    | Yes    |  |
^ Limit subvolume size          | Yes    | Yes    | ZFS: quota, BTRFS: quatagroup |
^ Linux root filesystem         | ?      | Yes    |  |
^ Striping                      |        |        |  |
^ Mirroring                     |        |        |  |
^ Redundancy on single disc     | Yes    | metadata| ZFS: copies=n param |
^ Online scrubbing              | Yes    | Yes    | scrub - scan and check data integrity |
^ In place ext2/3/4 conversion  | No     | <del>Yes</del>    | BTRFS: with rollback possible! DO NOT USE, it is not well tested and causes errors! |
^ maturity                      | Yes    | Linux 3.10 | |
^ GRUB loader support           |        | Grub2  |  |
^ Snapshots                     | Yes    | Yes    |  |
^ Performance                   | fuse   | kernel | fuse is anymore bottleneck with moder kernels |

^FS Overhead  ^^^
^    EXT4     ^     BTRFS     ^    ZFS    ^
|   270 371   |    269 540    |           |


[[http://richardhartmann.de/blog/posts/2012/02/RAID-sucks/]]

[[http://docs.oracle.com/cd/E37670_01/E37355/html/ol_use_case1_btrfs.html]]


Check and compare:
  * dedup: https://btrfs.wiki.kernel.org/index.php/Deduplication
  * single file compression (btrfs: chattr +c ...)
  * online convert from RAID0 to RAID1
  * direct mounting subvolumes (btrfs: by subvol path or subvol ID)
  * file snapshot (btrfs: cp --reflink /mnt/sv1/test1 /mnt/sv1/test3)
  * ZFS: online defrag (BTRFS: mount -o autodefrag)
  * btrfs: convert from ext4 (btrfs-convert /dev/sdb1) and rollback
  * btrfs as root
  * Locate modified files from last snapshot (btrfs subvolume find-new)
  * SSD upport (trim/discard)

===== ZFS =====
  * (-) compression on/off per subvolume - no support for +c attribute
  * (+) All features are controlled by subvolumes (datasets) attributes (compression, deduplication)
  * (-) CDDL license is not compatible with Linux kernel. Cannot be distributed as derived work.
  * (-) Only mirrored block devices can be removed. Non-redundant and raidz devices cannot be removed from a pool.
  * (-) Deduplication on block level, cannot find shifted blocks.

===== BTRFS =====
  * (+) compression on during mount, but also using attribs 
  * (?) deduplication not implemented. External tool available: [[https://github.com/markfasheh/duperemove]duperemove]. External tool can be also a benefit. To reduce CPU and memory you can start deduplication process when you want, and only on selected files/dirs.
  * (-) All features controlled by mount options
  * (+) Every block device can be removed, data are automatically copied (balanced) to free space on other devices
  * (+) Metadata are automatically duplicated between block devices, data are striped