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pages/04.other/05.btrfs/default.en.md

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+---
+title: BTRFS
+---
+
+[toc]
+## Utils
+`# pacman -S btrfs-progs`  
+
+## Fstab example
+`UUID=2dc70a6e-b4cf-4d94-b326-0ba9f886cf49 /mnt/tmp btrfs defaults,noatime,compress-force=zstd,space_cache=v2,subvol=@ 0 0`
+
+Options:  
+```
+defaults       -> Use whatever defaults
+noatime        -> Reading access to a file is not recorded
+compress-force -> Send all files through the compression algorithm
+space_cache    -> Increases performance by mapping unallocated blocks
+subvol         -> Subvolume to mount
+```
+
+## Filesystem usage
+Show storage allocated, used and free  
+`# btrfs fi usage (mountpoint)`  
+
+```
+allocated: space used
+unallocated: actual free space
+Used: amount of data stored
+Free: free storage based on "Used"
+```
+
+Start rebalance of datachunks filled less than 70%  
+`# btrfs balance start --b -dusage=70 -musage=70 (mountpoint)`  
+
+Check status of rebalance  
+`# btrfs balance status -v (mountpoint)`  
+
+## Disable CoW
+Disable copy on write for folders (Only works on new files)  
+`$ chattr +C (path)`  
+
+## Device errors
+Error counts for a given mountpoint  
+`# btrfs dev stat (mountpoint)`  
+
+## Compression
+
+### Algorithms
+```
+zlib: Slow, but strong compression, level 1-9
+lzo : Fastest, weak compression
+zstd: [Recommended] Medium, newer compression standard than the others, only works on newer kernels, level 1-15
+```
+
+Enable compression for existing files  
+`# btrfs filesystem defragment -r -v -c(alg) (path)`  
+*It is impossible to specify the level of compression wanted.*  
+
+Add `compress=(alg)` to `/etc/fstab`  
+
+To specify a level of compression (zlib and zstd) use `compress=(alg):(level)` in fstab.  
+For zstd compression it is recommended to use `compress-force=zstd:(level)`  
+
+## Subvolumes
+List  
+`# btrfs subv list (path)`  
+
+Create  
+`# btrfs subv create (path)`  
+
+Mount a subvolume  
+`# mount -o subvol=@(subvolname) /dev/sdXX /(mountpoint)`  
+
+## Snapshots
+TODO
+
+## RAID
+An array can be mounted by specifying one of its members.  
+`# mount /dev/sdXX /mnt`  
+
+All members of an array have the same UUID, which can be mounted through fstab.  
+
+### RAID 1
+On filesystem creation  
+`# mkfs.btrfs -m raid1 -d raid1 /dev/sdXX /dev/sdYY`  
+
+### RAID 5
+On filesystem creation  
+*It is recommended not to use raid5/6 for metadata yet*  
+`# mkfs.btrfs -m raid1 -d raid5 /dev/sdXX /dev/sdYY /dev/sdZZ`  
+
+### RAID 10
+On filesystem creation  
+`# mkfs.btrfs -m raid10 -d raid10 /dev/sdXX /dev/sdYY /dev/sdZZ /dev/sdQQ`  
+
+### Convert to single device
+First, the files have to be collected on one device.  
+*DUP on system and metadata should only be used on HDDs. Use single on SSDs*  
+`# btrfs balance start -f -sconvert=dup,devid=(id) -mconvert=dup,devid=(id) -dconvert=single,devid=(id) /(mountpoint)`  
+
+Now unused devices can be removed  
+`# btrfs device delete /dev/sdYY /(mountpoint)`  
+
+### Replace dying/dead device in RAID array
+Show arrays that are available  
+`btrfs fi show`  
+
+From my testing the log has to be dropped before btrfs will mount the incomplete array  
+`btrfs rescue zero-log /dev/sdXX`  
+
+Mount with these options to be able to fix it  
+`mount -o rw,degraded /(mountpoint)`  
+
+The ID has to be replaced with the ID of the **missing** device!  
+`btrfs replace start -B (id) /dev/sdYY /(mountpoint)`  
+
+Query the status of the repace  
+`btrfs replace status /(mountpoint)`  
+
+Balance the filesystem at the end  
+`btrfs balance /(mountpoint)`