====== File Systems ======

===== FAQ =====

==== Which file system should I use? ====

If you ask this question, probably the one which is default for your distribution or ext4.

Some good file systems and their usage:

^ ext4 | root, data |
^ [[btrfs]] | redundant data, file servers |
^ zfs | redundant data, file servers |
^ xfs | root, data |
^ f2fs | flash storage |
^ [[gluster|glusterfs]] | computer clusters |
^ ntfs | shared storage with windows (slow, because [[fuse]]) |

==== There's an error "out of space" but I still have space! ====

Could be that you ran out of inodes. Check with ''df -i''.

===== xfs =====

^ get label[(https://blog.khmersite.net/2019/10/how-to-label-xfs-filesystem/)] | ''%%xfs_admin -l /dev/sdb1%%'' |
^ change label | ''%%xfs_admin -L NEWLABEL /dev/mapper/NAME%%'' |

==== empty space is still recoverable! ====
SSDs do garbage collection differently, which is why dd if=/dev/true or scrub don't work properly.

  * ''[[https://man7.org/linux/man-pages/man8/xfs_scrub.8.html|xfs scrub]]'' can TRIM the SSD's free space
  * you can use a systemd timer (''fstrim.service'' / ''fstrim.timer'') to [[https://wiki.archlinux.org/index.php/Solid_state_drive#Periodic_TRIM|TRIM periodically]]
  * you can enable the discard mount option to TRIM immediately after deleting a file, which slows down deleting files a fair bit.
===== ext4 =====

=== init ext4 inodes on mkfs ===
lazy inode init makes the drive behave slowly on first mount
  mkfs.ext4 -E lazy_itable_init=0,lazy_journal_init=0 /dev/sdXY

=== directory index for a huge amount of files ===

Huge amount = >300k

mount with ''dir_index''

if the error ''EXT4-fs warning (device /dev/sdx): ext4_dx_add_entry: Directory index full!'' occurs, you probably have more than 2 million files in one directory, check with

<code>$ cd /var/
$ debugfs
debugfs> open /dev/sdd1
debugfs> cd log/
debugfs> htree .
[...]
Number of Entries (count): 508
Number of Entries (limit): 508
[...]</code>

and remedy with ''fsck.ext4 -yfD /dev/sdx1''

([[https://noqqe.de/blog/2012/03/08/a-byte-of-ext4-directory-indexing/|source]])

===== NTFS =====
For interoperability with Windows; is mounted with FUSE and therefore pretty slow.

Use mount options ''fmask=117,dmask=007'' so the executable bit isn't set on everything.

===== exFAT =====
  * [[https://unix.stackexchange.com/questions/355763/exfat-vs-ntfs-on-linux|exFAT vs NTFS on Linux]]

===== UDF =====
  * [[https://askubuntu.com/questions/27936/can-and-should-udf-be-used-as-a-hard-drive-format|Can and should UDF be used as a hard drive format?]]
  * [[https://github.com/JElchison/format-udf|Format UDF]]