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linux:fs:btrfs [2017/06/19 08:50] – [periodic scrub] niziaklinux:fs:btrfs [2021/05/02 11:34] (current) – niziak
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 +====== BTRFS ======
 +
 ===== References ===== ===== References =====
 [[https://www.howtoforge.com/a-beginners-guide-to-btrfs]] \\ [[https://www.howtoforge.com/a-beginners-guide-to-btrfs]] \\
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 or or
 <code>mount /dev/loop1 /BTRFS</code> <code>mount /dev/loop1 /BTRFS</code>
 +
 +===== Swap support =====
 +
 +**Current state:** Do not create SWAP files on BTRFS!
 +
 +Swap support was restored with Kernel 4.21
 +
  
 ===== Add/remove block devices ===== ===== Add/remove block devices =====
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 !!! It is possible to remove any device if there is free space to which data can be moved during removal. !!! It is possible to remove any device if there is free space to which data can be moved during removal.
  
-===== Compression ===== 
- 
-[[https://btrfs.wiki.kernel.org/index.php/Compression]] 
- 
-Compression: 
-  * ZLIB -- slower, higher compression ratio (uses zlib level 3 setting) 
-  * LZO -- faster compression and decompression than zlib, worse compression ratio, designed to be fast  
- 
-Default compression for kernels up to 3.6 it's ZLIB. For compatibility with old kernel ZLIB is default. 
-LZO is fast and new algo, but can be buggy. 
- 
- 
-[[https://btrfs.wiki.kernel.org/index.php/FAQ#Does_a_balance_operation_recompress_files.3F|Does a balance operation recompress files?]] 
->No. Balance moves entire file extents and does not change their contents. If you want to recompress files, use btrfs filesystem defrag with the -c option. 
->Balance does a defragmentation, but not on a file level rather on the block group level. It can move data from less used block groups to the remaining ones, eg. using the usage balance filter. 
- 
-NOTE: Defragmentation with recompression destroys deduplication. 
-  * Size changed from 6,94 GB to 7,39 GB 
-  * After deduplication with 1024k block drops to 7.17 GB (net change in shared extents of: 490.0M) 
-  * After deduplication with 4k block drops from 7.17 GB to 6,94 GB(a net change in shared extents of: 306.6M) 
- 
-==== mount options ==== 
-Can be enabled during mount time: 
-<code bash> 
-mount BTRFS -o remount,compress=zlib 
-mount BTRFS -o remount,compress-force=zlib 
-</code> 
-> if the first portion of data being compressed is not smaller than the original, the compression of the file is disabled -- unless the filesystem is mounted with compress-force 
- 
-**compress-force=<method>** - Enable compression even for files that don't compress well, like videos and dd images of disks.  
- 
-Test data of size 651MB takes 371MB after compression. 
- 
-==== chattr +c ==== 
-Also single file compression possible using ''chattr +c filename.txt'' 
- 
-To recompress exisitng files, start defragmentation with -c param: 
-<code>btrfs filesystem defrag -c file.iso</code> 
-<code>btrfs filesystem defrag -c -r mydir</code> 
- 
-It is not possible to get compression ratio of file. 
- 
-Internals: 
-  * In compressed extents, individual blocks are not compressed separately; rather, the compression stream spans the entire extent. 
-  * BTRFS: There is a simple decision logic: if the first portion of data being compressed is not smaller than the original, the compression of the file is disabled -- unless the filesystem is mounted with compress-force 
- 
-==== btrfs property ==== 
-<code bash> 
-btrfs property set <file> compression <zlib|lzo> 
-</code> 
-===== Deduplication ===== 
-External tool to find duplicated extens available 
-[[https://github.com/markfasheh/duperemove]] 
- 
-Simply do 'make' and 'make install' 
-Following binaries will be installed: 
-  * btrfs-extent-same 
-  * csum-test 
-  * duperemove 
-  * hashstats 
-  * show-shared-extents 
- 
-Recursively find duplicates in <dir> 
-<code>duperemove -r <dir></code> 
- 
-The same as above, but make real deduplication (on BTRFS only) 
-<code>duperemove -rd <dir></code> 
- 
-Increase deduplication chance by reducing block size to 4k: 
-<code>duperemove -b 4k -rd <dir></code> 
- 
-This deduplication works nice, it can find some shared parts inside Maildir. 
- 
- 
-===== Subvolumes ===== 
- 
-<code> 
-btrfs subvolume create /BTRFS/sub1 
-btrfs subvolume create /BTRFS/sub2 
-btrfs subvolume create /BTRFS/sub3 
-</code> 
- 
-<code> 
-btrfs subvolume list /BTRFS 
-ID 256 gen 234 top level 5 path sub1 
-ID 257 gen 227 top level 5 path sub2 
-ID 258 gen 228 top level 5 path sub3 
-</code> 
- 
-Mount subvolume 
-<code>mount -o subvol=sv1/sv12 /dev/sdb /mnt</code> 
- 
-Getting data size on each subcvolume: 
-  * Enable quota on btrfs ''btrfs quota enable /'' 
-  * Install script [[https://github.com/agronick/btrfs-size]] 
- 
- 
-==== Different mount options ==== 
-NOT SUPPORTED YET: 
-  In general, btrfs doesn't _yet_ have the runtime infrastructure to handle  
-  per-subvolume mount options.  The on-device format and general approach  
-  in the kernel was designed to allow it, and it's on the roadmap, it just  
-  hasn't been done... yet. 
- 
-To make workaround it is possible to use attributes on files or directories: 
-  * C disable COW feature (for newly created directories or zero sized files). New files in directores with C attributes will be created with C attrib. But not subdirectories. 
-  * c enable compression 
- 
-==== Move data between subvolumes ==== 
-See `cp` command arg: 
-  When --reflink[=always] is specified, perform a lightweight copy, where the data blocks are copied  only  when  modified.   If  this  is  not  possible  the  copy  fails,  or  if 
-       --reflink=auto is specified, fall back to a standard copy. 
- 
-<code bash> 
-cp -pr --reflink=always srcDirectory dstDirectory/ 
-rm -r srcDirectory 
-</code> 
  
 ====== Scrub ====== ====== Scrub ======
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 <code bash>btrfs scrub status /</code> <code bash>btrfs scrub status /</code>
  
-===== periodic scrub ===== 
  
-From arch linux ''btrfs-progs''+====== migration to BTRFS ======
  
-<file | /etc/systemd/system/btrfs-scrub@.service> +<code bash>apt-get install btrfs-tools</code>
-[Unit] +
-Description=Btrfs scrub on %f+
  
-[Service] +====== Issues ======
-Nice=19 +
-IOSchedulingClass=idle +
-ExecStart=/bin/btrfs scrub start -B %f +
-</file>+
  
-<file | /etc/systemd/system/btrfs-scrub@.timer> +===== Compression type 0x3 not supported =====
-[Unit] +
-Description=Monthly Btrfs scrub on %f +
- +
-[Timer] +
-OnCalendar=monthly +
-AccuracySec=1d +
-Persistent=true +
- +
-[Install] +
-WantedBy=multi-user.target +
-</file>+
  
 +GRUB 2.02 doesn't support ZSTD compression.
 +Solution is to exlude ''/boot'' from ZSTD compression (below) or install more recent Grub (from Debian Bullseye)
 <code bash> <code bash>
-systemctl daemon-reload +sudo btrfs filesystem defragment -v -r -czlib /boot 
-systemctl enable btrfs-scrub@-.timer +sudo btrfs property set /boot compression zlib 
-systemctl start btrfs-scrub@-.timer+# disable compression for newly created files 
 +chattr -Rc /boot
 </code> </code>
- 
- 
-====== migration to BTRFS ====== 
- 
-<code bash>apt-get install btrfs-tools</code> 
- 
-====== Issues ====== 
  
 ===== error inheriting props for ino 3336468 (root 264): -28 ===== ===== error inheriting props for ino 3336468 (root 264): -28 =====