I've been trying out the Btrfs with an SSD drive and like the compress option which is set in the fstab.
However this only applies to the files created after I have installed the operating system and modified the fstab file.
What I would like is to apply the compression to all the files on the system, to see if it improves boot time and application start up times.
Does anybody know of a way that I could apply the change to all files either pre or post installation?
I believe you have to run
btrfs fi defragment
after mounting the FS with compression.
Check this out: https://askubuntu.com/questions/129063/will-btrfs-automatically-compress-existing-files-when-compression-is-enabled
When installing you can issue a:
mount -o remount,compress=lzo
Often you will have to do it just as the installer starts installing stuff (maybe you will miss a file or 2. but no biggie). You could check to see if the installer has already mounted the filesystem just before the install stage.
Also make sure you update the /etc/fstab on the installed system. I use the following options that give some other improvements:
compress=lzo,ssd,relatime,space_cache,inode_cache,autodefrag
You can also try using compress-force=lzo for the install rather than compress=lzo, it makes sure that even files that don't compress that well are still compressed. That would make writes slower but since it's a one time install that might be worth it. But I'm not sure if it improves reads or not.
I have seen another way that involves renaming the mount.btrfs binary and replacing it with a script but when I did it under Ubuntu it messed up as it normally installs to subvolumes @ and @home but everything just got dumped to the root of the filesystem.
Alternatively you can install and then use the defragment, but you must defragment every file individually as the command isn't recursive. This could come in handy to upgrade to the new compression methods that are likely to appear in the newer versions of btrfs, snappy and lz4. Run the following from the / directory.
find -xdev -type f -exec btrfs fi defrag '{}' \;
Like many questions with software - the answers change depending on WHEN they get asked/answered. I'm freshening the answer to help anyone Googling their way into topic. :)
The correct answer for btrfs 3.12 and higher to compress directories/mountpoints POST installation (the required recursive option for defrag was added with btrfs 3.12 released in Nov 2013) :
btrfs filesystem defragment -c -r MOUNTPOINT
Here is the current options from the cli of btrfs version 4.4:
btrfs filesystem defragment
usage: btrfs filesystem defragment [options] | [|...]
Defragment a file or a directory
-v be verbose
-r defragment files recursively
-c[zlib,lzo] compress the file while defragmenting
-f flush data to disk immediately after defragmenting
-s start defragment only from byte onward
-l len defragment only up to len bytes
-t size target extent size hint
BTRFS Use Case from their wiki for using the recursive param to defrag directories/mount points
