IntroductionHappy 2020 chaps!It’s January again, and it’s exam time for me, which means procrastination. And what better way to procrastinate than exploring something awesome likeBTRFS snapshots?In this blog post I’ll share why I migrated fromLVM EXT4toBTRFSand the benefits I found. I’ll go briefly through my experience with BTRFS and I’ll also share a tool I found recently - Snapper - which makes snapshotting even easier so let’s get started!My experience with EXT and LVMMost, if not all modern linux distributions use EXT4 as adefaultfilesystem for their installation.EXT4 came out in 2006 as anupgradeto EXT3. It added some optimizations and “trim” changes but nothing sensational. EXT3 came out in November 2001 and, similarly to EXT4, was an upgrade to the previous generation - EXT2. EXT2 is the father of all EXT filesystems (there is just EXT but you’ll probably never see one in use anymore) and it has come out in 1993!Now, maturity is a very good thing to have when speaking about filesystems - after all, you don’t want to invest millions in changing the filesystem on all of your production servers only to find out that it’s unstable or its performance is not as good as you expected. Even if you don’t have millions of servers, why should you bother to change the filesystem on your laptop with a filesystem still considered “unstable” by some when EXT is working just fine?Personally, I have been an EXT user for years. Initially, I was using plain EXT, back when I was dual-booting Windows but then I never quite got disk partitioning right. I always found myself with a least a dozen of partitions which was quite annoying. What’s more, EXT4 supportsonly offlineshrinking which is quite annoying because even if you use LVM, you still have to unmount the EXT4 partition to reduces its size! Here’s a neat table comparing some of the features of the hottest filesystems right now:Mini rant on EXT4 and LVM EXT4For some time I was using LVM EXT4. This solved the many partitions problem as I could justextendthe volumes with the new free space that I had added and then run a simpleresize2fson the EXT partition.Following that I started using LUKS forfull disk encryptionwhich isa must have nowadays. Resizing partitions got even more difficult as to simply add more space to my EXT partition, I had to boot into a live environment, extend the LUKS-encrypted partition, then increase the size of the physical LVM volume, then increase the size of the logical LVM volume and finallyresize2fsthe EXT partition. What a pain that was!At this point doing anything on the filesystem level was an enormous pain.The final thing the made me look for alternatives wasbackups. I started doing regular backups of my work and I wanted to keep my backup procedure as simple as possible. Plainrsync-ing was doing sort of alright. I used a wrapper application - backintime - as I had some permissions-related issues whenrsync-ing only. For most of the time this approach was doing well. It had occasional misfortunes -backintimehardlinks all files to represent a full directory tree on the backup location and only copies the changes which works well, however, if the backup is interrupted, sometimes it cannot continue and starts copying overall filesfrom scratch.This made backups clumsy and always made me think twice before putting my computer to sleep. Furthermore, how do you restore restore the backups withnodowntime? Another feature I was missing was being able to restore from bad commands - sometimes I run commands or scripts that happen to misbehave and there was no easy way to revert their actions. Doing a full backup just for that single script is not really worth it. Sure, LVM supports snapshots but then again restoring snapshots can only be done when the LVM partition is not mounted and that’s a pain…Some light in the end of the filesystems tunnel - BTRFSAfter checking out a few filesystems I decided to onboard the BTRFS hype train!BTRFS solves all the problems I had so far:supportsonlineresizing - both extending and shrinkinghas built-in support for snapshots - useful for both backups and “testing out” scriptsremoves the need for LVM and thus eliminates 1 layer for filesystem-ing (if that’s a word)On top of that, in 2008, the principal developer of EXT3 and EXT4 - Theodore Ts’o stated that although ext4 has improved features, it is not a major advance; it uses old technology and is a stop-gap. Ts’o said that BTRFS is the better direction because “it offers improvements in scalability, reliability, and ease of management”.On the downsides, there isn’t a built-in support for encryption so LUKS has to stay for now, although that feature is planned to come at some point in the future. Another question mark was performance - from the research I did, BTRFS was doing as good as EXT4 and ZFS, if not better on some benchmarks. It seemed to be struggling on RAIDs and on spinning hard drives because of fragmentation. But it’s 2020 - if you’re still using such a drive you have bigger issues that the performance of the filesystem…You said BTRFS snapshots?Now onto the good stuff. The arch wiki contains some excellent documentation (as always) on BTRFS and everything that you might want to do with it. I highly recommend going through it. There’s no point of copying the commands from there since I probably won’t do better at explaining them than they have so definitely have a read.BTRFS (B-Tree Filesystem) utilizes B-Trees and there are some interesting consequences from that. For example, every node in the filesystem is either aleafor atree. If you are familiar with Trees, you have an idea about their recursive nature. This allows BTRFS to have subtress which are also BTRFS nodes. Surprise, surprise, these nodes are calledsubvolumes in BTRFS terminology. Snapshots are also a type of subvolumes. Snapshots represent the current state of the filesystem and essentially are just another node in the tree. Since BTRFS is a CoW filesystem, snapshots are cheap to create and maintain and you can easily go back to a snapshot if you like. Creating a snapshot is easy as$ sudo btrfs subvolume snapshot /some subvolume name /snapshots subvolume destinationYou can find what subvolumes you have by running:$ sudo btrfs subvolume list /You canmountandbrowseyour snapshots as if it was the real subvolume! Any changes you make on the original subvolume is not reflected on the snapshot effectively giving you a way togo back in time for free! What’s even more awesome is that you candifftwo snapshots! For instance, if you want to run some dodgy script, or install some application, you can snapshot before doing the operation, do the operation and snapshot again. Then you candiffthebeforeandaftersnapshots to see what’s changed. How awesome is that!The CLI tool for managing BTRFS is called, logically,btrfsand has loads of options. If you can’t be bothered to learn all of them, there is a pretty neat tool called snapper which manages snapshots for you. I’d recommend reading the manpage forsnapper.I’ll share the getting started part and the way I’m using it on my machine.Let’s play with Snapper and snapshotsFirstly install snapper. Snapper is included in dnf’s repositories:$ sudo dnf install -y snapperTo operate,snappermakes use of configs. Each BTRFS subvolume that you want to snapshot withsnappermust have a corresponding config. I have my/homedirectory in a separate BTRFS subvolume. To create config for it, you can run$ sudo snapper create-config /home(optional) Now if you want to run all the snapper commands on that config, without sudo, you’ll need to add your user to theALLOWED_USERSlist in/etc/snapper/configs/homefile. Mine looks like this:... # users and groups allowed to work with config ALLOW_USERSviktor ALLOW_GROUPSviktor ...Now you can usesnapperto manage snapshots for the/homeconfig without sudo. Every time you usesnapperwith the non-default config (root) you need to specify it with-cargument. To see available snapshots on the/homeconfig we just made, run$ snapper -c home listThis command prints the following table:# | Type | Pre # | Date | User | Cleanup | Description | Userdata ------------------------------------------------------------- 0 | single | | | root | | current |When you make snapshots, more entries will appear in this table. You can add new snapshots by running$ snapper -c home createEasy as that! Now acopyof your/homesubvolume has appeared in/home/.snapshots$ tree /home/.snapshots -L 3 /home/.snapshots └── 1 ├── info.xml └── snapshot └── viktorListing available snapshots now shows the new snapshot we just added:# | Type | Pre # | Date | User | Cleanup | Description | Userdata ------------------------------------------------------------------------------------------ 0 | single | | | root | | current | 1 | single | | Sun 12 Jan 2020 11:23:01 PM GMT | viktor | | |You can delete a snapshot withsnapper -c home delete snapshot numbere.g:$ snapper -c home delete 1Note: I don’t recomment deleting the snapshot with id 0 as that’s your current tree and wil result in data lossYou can use these snapshots as backups at any single point of time. Also you canrsyncthem to a remote server if you want to be safe in case your disk fails.I wrote the following wrapper aroundsnapperto wrap a command in snapshots. The idea being is - let me see what happens if I run this command.function snp(){ # Runs a command wrapped in btrfs snapper pre-post snapshots. # Usage: $ snp commands # e.g.: $ snp sudo dnf install htop cmd$ snapshot_nbr$(snapper -c home create --typepre --cleanup-algorithmnumber --print-number --description${cmd}) eval $cmd snapshot_nbr$(snapper -c home create --typepost --cleanup-algorithmnumber --print-number --pre-number$snapshot_nbr) }This function creates apretype snapshot before running the command, runs the command you give it and then does aposttype snapshot. Runningsnp echo World /home/viktor/testcreates the following snapshots# | Type | Pre # | Date | User | Cleanup | Description | Userdata ---------------------------------------------------------------------------------------------------------------- 0 | single | | | root | | current | 1 | pre | | Mon 13 Jan 2020 12:06:16 AM GMT | viktor | number | echo World /home/viktor/test | 2 | post | 1 | Mon 13 Jan 2020 12:06:16 AM GMT | viktor | number | |What’s great is I can see what files have changed by running:$ snapper -c home status 1..2 c..... /home/viktor/testWe can even diff the 2 snapshots!$ snapper -c home diff 1..2which literally runs/usr/bin/diff(or anything you tell it to) on the 2 snapshots:--- /home/.snapshots/1/snapshot/viktor/test 2020-01-13 00:06:03.081757300 0000 /home/.snapshots/2/snapshot/viktor/test 2020-01-13 00:06:16.589780114 0000 -1 1,2 Hello WorldYou can undo the changes made by running:$ snapper -c home undochange 1..2 create:0 modify:1 delete:0and now all the changes we made are reversed - how awesome is that! You can even specify which files to revert if you don’t want to revert all changes.With all those features, literally the sky is the limit to what you can do!Useful materialsI really liked this talk on BTRFS - https://www.youtube.com/watch?v-m01x3gHNjgt0sThe Arch wiki has a good guide on BTRFS - https://wiki.archlinux.org/index.php/BtrfsThe snapper docs have a decent tutorial on what you can do how - I recommend going through it - http://snapper.io/tutorial.htmlAlso, the arch wiki has a tutorial onsnapperthat’s also worth a read - https://wiki.archlinux.org/index.php/SnapperI’ll leave it up to you to experiment with and share your experience in the comments. Thank you for reading and till next time :)