Comment by lproven

Comment by lproven 2 days ago

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To be fair, your statement could be edited as follows to increase its accuracy:

> btrfs is quite infamous for eating your data.

This is the reason for the slogan on the bcachefs website:

"The COW filesystem for Linux that won't eat your data".

https://bcachefs.org/

After over a decade of in-kernel development, Btrfs still can't either give an accurate answer to `df -h`, or repair a damaged volume.

Because it can't tell a program how much space is free, it's trivially easy to fill a volume. In my personal experience, writing to a full volume corrupts it irretrievably 100% of the time, and then it cannot be repaired.

IMHO this is entirely unacceptable in an allegedly enterprise-ready filesystem.

The fact that its RAID is even more unstable merely seals the deal.

f_devd 2 days ago

> Btrfs still can't either give an accurate answer to `df -h`, or repair a damaged volume.

> In my personal experience, writing to a full volume corrupts it irretrievably 100% of the time, and then it cannot be repaired.

While I get the frustration, I think you could have probably resolved both of them by reading the manual. Btrfs separates metadata & regular data, meaning if you create a lot of small files your filesystem may be 'full' while still having data available; `btrfs f df -h <path>` would give you the break down. Since everything is journaled & CoW it will disallow most actions to prevent actual damage. If you run into this you can recover by adding an additional disk for metadata (can just be a loopback image), rebalancing, and then taking steps to resolve the root cause, finally removing the additional disk.

May seem daunting but it's actually only about 6 commands.

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  • lproven a day ago

    Hi. My screen name is my real name, and my experience with Btrfs stems from the fact that I worked for SUSE for 4 years in the technical documentation department.

    What that means is I wrote the manual.

    Now, disclaimer, not that manual: I did not work on filesystems or Btrfs, not at all. (I worked on SUSE's now-axed-because-of-Rancher container distro CaaSP, and on SLE's support for persistent memory, and lots of other stuff that I've now forgotten because it was 4 whole years and it was very nearly 4 years ago.)

    I am however one of the many people who have contributed to SUSE's excellent documentation, and while I didn't write the stuff about filesystems, it is an error to assume that I don't know anything about this. I really do. I had meetings with senior SUSE people where I attempted to discuss the critical weaknesses of Btrfs, and my points were pooh-poohed.

    Some of them still stalk me on social media and regularly attack me, my skills, my knowledge, and my reputation. I block them where I can. Part of the price of being online and using one's real name. I get big famous people shouting that I am wrong sometimes. It happens. Rare indeed is the person who can refute me and falsify my claims. (Hell, rare enough is the person who knows the difference between "rebut" and "refute".)

    So, no, while I accept that there may be workarounds that a smart human may be able to do, I strongly suspect that these things are accessible to software, to tools such as Zypper and Snapper.

    In my repeated direct personal experience, using openSUSE Leap and openSUSE Tumbleweed, routine software upgrades can fill up the root filesystem. I presume this is because the packaging tools can't get accurate values for free space, probably because Btrfs can't accurately account for space used or about to be used by snapshots, and a corrupt Btrfs root filesystem can't be turned back into a valid consistent one using the automated tools provided.

    Which is why both SUSE's and Btrfs's own docs say "do not use the repair tools unless you are instructed to by an expert."

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    • f_devd 5 hours ago

      Hey. That's sounds like an awful experience. Btrfs has some rough edges especially since a lot of maintenance tasks are "manual", and you are right to try and address it. And it's annoying that becomes personal for some people with too much time.

      For my perspective, my experience with btrfs has been flawless through 11 machines and at least 3 major releases on each without any maintenance but it could just be I'm not hitting the worst case (only use snapshots on 2 machines, raid on 3). And I've only used btrfs since fairly recently (~4 years now). I've had to recover one drive of a friend using the method I outlined before as he filled the entire drive with media. For me the trade-off of a few rough edges but more functionality & flexibility than other filesystems is worth it.

      For your update issue, I think you're mostly correct; the package manager likely assumes the filesystem is not snapshotted (i.e. it will reclaim disk space), while btrfs with snapshots/CoW will use the entire size of written files unless it's in the same snapshot.

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      • lproven 4 hours ago

        Thanks for that response.

        It's a balance. All of life is a balance.

        I worked at Red Hat very briefly, and for SUSE for longer than ever before. Both were good workplaces with a good atmosphere: RH is one of the friendliest places ever, and I'm still friends with former colleagues from over a decade ago.

        OTOH, installing Fedora 14 was like having a bucket of cold water to the face. I used and reviewed Red Hat Linux in the 1990s and it was a massive PITA. It had no automatic dependency resolution, so complex software installation (e.g. going from KDE 1.x to KDE 2.x) was a huge task involving manually installing hundreds of dependencies.

        RH would not bundle KDE (because Qt was not 100% FOSS) -- which is also why Mandrake was founded -- and so the GUIs on RHL were poor.

        I switched to SUSE. Good package management, good GUIs, good system-management tools. (YaST was way better than RH's inadequate `linuxconf`.)

        RH "fixed" this by... removing Linuxconf.

        Trying Fedora a decade later and it was just as bad. All the external bits improved because upstream improved. GNOME was still a mess. KDE had got much more bloated. Xfce was better than ever.

        But the RH in-house bits, while having nice visual design, were functionally terrible. The installer was an embarassment.

        Over a decade of work since I reviewed RHL 9 and it was worse than ever.

        A few years later, go to work at SUSE, and hey, openSUSE was lovely. All the good bits still there and improved. Yeah, a bit bigger and slower and clunkier than Ubuntu.

        But there's always a downside.

        An older team so less party atmosphere. Fewer "team building" sessions in the pub.

        And while I was away, SUSE switched from ReiserFS to Btrfs, and as usual, SUSE of old being fond of experimental bleeding-edge filesystems, it's half-implemented and doesn't work right.

        Snapper doesn't prune snapshots thoroughly enough. It fills your disk and because of unimplemented or non-working features it can't tell when this will happen.

        Official SUSE answer: give it lots of space. Here, our FS falls over unrepairably when full, so give it all your space so it won't fill up! And you can't repair it so take lots of backups!

        Every distro has downsides. Every filesystem has downsides but they are much less obvious.

        Btrfs made my openSUSE boxes collapse and crash 2-3 times a year for 4 years. That is intolerable. I put up with that kind of crashy junk in 1997 or so but not 20 years later.

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