[lloeki]

> On a related note: Never ever use the ext4 to btrfs conversion tool! It's horribly broken and causes issues weeks later.

Care to give some details about this and other failures? Part of what makes a FS reputation is not just people telling "it works" but also stories about how the thing crashed and how they recovered from it. IOW, it always works, until it doesn't, and then it still "works" because I can dig myself out of the hole this or that way.

Inspired by the way you can convert a Debian VM to Arch Linux on Digital Ocean, I happen to have been toying with it recently to auto-convert a blank Debian 8.x VM from ext4 to btrfs. Looks like things are fine, but only because the kernel is <4.x and the VM has very little data on it since it's blank.

WARNING: This is a toy. Do not use for production.

https://github.com/lloeki/digitalocean-ext4-to-btrfs

[eeZi]

It resulted in random, hard to reproduce ENOSPC errors down the line without either data or metadata being anywhere close to full. Neither us nor the btrfs developers that took a look at it were able to figure out what exactly went wrong, but it was something about new blocks not fitting anywhere despite lots of free space.

Someone on #btrfs said that the filesystem layout is a lot different when using the conversion tool and all of the regression testing happens with regular filesystems, not converted ones.

We reinstalled all machines from scratch. Never happened again.