btrfs

When you modify a file on btrfs, what happens to the original disk blocks holding that data?

A colleague assumes btrfs is the universally adopted next-gen Linux filesystem. Where does the vendor picture actually diverge?

You suspect corruption on a btrfs filesystem and want to run a consistency check. What is the one hard precondition, and how do you actually make it repair errors?

You want to store a large database file or a VM disk image on btrfs without the usual COW fragmentation penalty. What do you set, and what is the catch on an existing non-empty file?

You mount a btrfs filesystem with compress=zstd and expect all existing files to shrink. Which files actually get compressed?

In btrfs terms, what is a subvolume, and how is it different from just making a directory?

When you list subvolumes, the top-level root subvolume never appears in the output. What ID does it always carry, and why does that matter?

The word snapshot means an immutable frozen image in LVM. What is fundamentally different about a btrfs snapshot?

How do you create a btrfs snapshot of a subvolume, and how do you get a read-only one for backups?

A btrfs filesystem is running low on space. What is the simplest way to grow it, and what does it require you to reformat?

One disk in a btrfs RAID-1 array has failed. What mount option lets you access the data, and what is the sequence to fully restore redundancy?

Why can df -h report misleading free space on a btrfs filesystem, and which commands give a trustworthy picture?

How does openSUSE's default btrfs setup let you roll back the system after a bad admin change without also reverting your personal files?

You're managing btrfs snapshots on openSUSE with Snapper from the command line. What does snapper rollback do that snapper delete and snapper create don't?

When sizing a partition for btrfs versus ext4, why should you deliberately allocate more space than usual?

Fedora also defaults to btrfs, but its layout is far simpler than openSUSE's. What does a default Fedora btrfs install actually configure?

What capabilities does btrfs provide on its own that ext4 or xfs only get by stacking external layers like LVM and mdadm?

You run a bare mkfs.btrfs /dev/sdb1 on a single disk. What checksum and metadata profile does it pick by default?

After lvextend grows the logical volume under a btrfs filesystem, how do you make btrfs use the new space — and how would you instead shrink it?

btrfs offers compress=lzo, zlib, and zstd. How do they trade off, and when does compression actually make disk access faster rather than merely smaller?

You're deciding which directories to mount with btrfs compress. Where does it pay off, and where is it pointless or harmful?

A subvolume you created isn't the default one. How do you mount it, and how do you change which subvolume mounts by default?

What must be true before btrfs subvolume delete works, and why doesn't the freed space come back right away?

A btrfs snapshot is 'treated like a subvolume' internally. What practical consequence does that have, and what does a snapshot NOT capture?

You just ran btrfs device add to grow a filesystem. Is running btrfs filesystem balance afterward worth it?

What does btrfs device delete /dev/sdb1 /mnt/btrfs/ do before it actually detaches the disk, and why can it be very slow?

After rebooting a machine with a multi-device btrfs filesystem, what command must run so btrfs can assemble it?

An openSUSE update leaves the system unbootable. How can btrfs snapshots get you booted again without a rescue disk?

Where does openSUSE's Snapper keep its configuration, and how many snapshots does it retain by default?

Beyond snapper rollback, what do snapper cleanup and snapper undochange each do?

How do you find out how much disk space a single btrfs subvolume or snapshot uses, and what's the difference between the rfer and excl columns?

When you build a multi-device btrfs with mkfs.btrfs, what do the -d and -m options control, and what happens if you skip them?

Which package do you install to get the btrfs and mkfs.btrfs commands, and why can't you just memorize one name?

What do the -a, -p, and -t flags add to btrfs subvolume list?

How do you measure how much space btrfs transparent compression is actually saving you?

In compsize output, why can the Referenced column be larger than Uncompressed, and what does that reveal about how btrfs stores mostly-empty files?

openSUSE's automatic snapshots are eating your disk. What three separate changes fully turn them off?