BCacheFS is being disabled in the openSUSE kernels 6.17+
lwn.net
lwn.net
As I predicted, out of tree bcachefs is basically dead on arrival - everybody interested is already on ZFS, btrfs is still around only because ZFS can't be mainlined basically
ZFS is extremely annoying with the way it does extend and the fact that you can’t mismatch drive size. It’s not a panacea. There clearly is space for an improved design.
[1]: https://hexos.com/blog/introducing-zfs-anyraid-sponsored-by-...
It clearly is an acceptable one for a lot of people but it does leave space for alternative designs.
I then had to manually delete the file with the I/O error (for which I had to resovle the inode number it barfed into dmesg) and try again - until the next I/O error.
(I'm still not sure if the disk was really failing. I did a full wipe afterwards and a full read to /dev/null and experienced no errors - might have just been the meta-data that was messed up)
Over the last one or two years I've experienced twice a checksum mismatch on the file storing the memory of a VMWare Workstation virtual machine.
Both are very likely bugs in Btrfs, and it's very unlikely that have been caused by the user (me).
In the relatively far past (around 5 years ago), I've had the system (root being on Btrfs) turning unbootable for no obvious reason, a couple of times.
Despite not being directly used, these blocks are kept (and cannot be reused) because another part of the extent they belong to is actually used by files.
This can happen if a large file is written in one go, and then later one block is overwritten - btrfs may keep the old extent which still contains the old copy of the overwritten block.The question was around usage, because without knowing people's usecases and configurations it'll never be usable for you while working fine for others.
As usual with all these Linux debates, there's a loud group grinding their old hatreds that can be decade old.
If 0.1% of users say it corrupted for them, and then don't provide any further details and no one can replicate their scenario then it does make it hard to resolve it
there's a feedback effect: if users know that a filesystem takes these kinds of issues seriously and will drop what they're doing and jump on them, a lot of users will very happily spend the time reporting bugs and working with devs to get it resolved.
people don't like wasting their time on bug reports that go into the void. they do like contributing their time when they know it's going to get their issue fixed and make things better for everyone.
this is why I regularly tell people "FEED ME YOUR BUG REPORTS! I WANT THEM ALL!"
it's just what you have to do if you want your code to be truly bulletproof.
No, Kent, they are not. Posting attacks like this without evidence is cowardly and dishonest. I'm not going to tolerate these screeds from you about people I've worked with and respect without calling you out.
Every time you spew this toxicity, a chunk of bcachefs users reformat and walk away. Very soon, you'll have none left.
It doesn't matter if you want to "tolerate" it if every time there's a filesystem thread there's stories about lost filesystem and unfixed bugs, and the rare times people try to report bugs or issues they go nowhere.
You're ranting about reality, and somehow I doubt you were ever a user of mine.
I've worked hard to establish an engineering community where no one has to be afraid to point out broken shit, including and especially in my code, and I wouldn't want your attitude anywhere near it.
Absolutely. Demonstrably much moreso than you over the past decade.
> I've worked hard to establish an engineering community where no one has to be afraid to point out broken shit,
You have failed. Look at this conversation: https://lore.kernel.org/lkml/fe51512baa18e1480ce997fc535813c...
Do you think Arnd, David, and Russell feel like they were rewarded for pointing out your broken shit? I doubt it. I certainly don't. You were so completely and obviously in the wrong there I have difficulty believing it was real.
I'm not replying to you again. Good luck :)
Not comparable to losing filesystems, sorry...
Also, filesystems just work. Nobody is gonna say "oh I'm using fileystem X and it works!" because that's the default. So, naturally, 99% of the stuff you'll hear about filesystems is when they don't work.
Don't believe me? Look up NTFS and read through reddit or stackexchange or whatever. Not a lot of happy campers.
I don't.
It's also the reason I am completely against the Debian "backporting" methodology to pretend they aren't using the new version of something.
Debian doesn't "backport" anything, they ship upstream LTS kernels straight, so please stop spreading this misinformation.
For some bizarre reason I can't conceive people not only believe but also keep complaining that Debian ships franken-kernels like RHEL does. See [0] for another instance.
Is it wrong to ask how to reproduce an issue?
It's generally fine if you stay on the happy path. It will work for 99% of people. But if you fall off that happy path, bad things might happen and nobody is surprised. In my personal experience, nobody associated with the project seems to trust a btrfs filesystem that fell off the happy path, and they strongly recommend you delete it and start from scratch. I was horrified to discover that they don't trust fsck to actually fix a btrfs filesystem into a canonical state.
BCacheFS had the massive advantage that it knew it was experimental and embraced it. It took measures to keep data integrity despite the chaos, generally seems to be a better design and has a more trustworthy fsck.
It's not that I'd trust BCacheFS, it's still not quite there (even ignoring project management issues). But my trust for Btrfs is just so much lower.
Btrfs has destroyed itself on my testing/lab machines three times during last two years up to point where recovery wasn’t possible. Metadata corruption being main issue (or that’s how it looks like to me at least).
As of now I trust BCacheFS way more. I’ve given it roughly the same time to prove itself as Btrfs too. BCacheFS has issues but so far I’ve managed to resolve them without major data loss.
Please note that I currently use ext4 in all ”really important” desktop/laptop installations and OpenZFS in my server. Performance being the main concern for desktop and reliability for server.
bcachefs isn't going away.
The SuSE guy also reversed himself after I asked; Debian too, so we have time to get the DKMS packages out.
I don't plan on giving ZFS or other filesystems not designed for Linux another go.
source: worked as a support engineer for a block storage company, witnessed hundreds of customers blowing one or both of their feet off with ZFS.
(Legitimate question: I manage several PB with ZFS and would like to know where I should be more cautious.)
There were legitimate bugs in ZFS that we hit. Mostly around ZIL/SLOG and L2ARC and the umpteen million knobs that one can tweak.
You can do the same with just about any file system. In the Windows world you can blow your feet off with NTFS configuration too.
Of course there have been bugs, but every filesystem has had data-impacting bugs. Redundancy and backups are a critical caveat for all file systems for a reason. I once heard it said that “you can always afford to lose the data you don’t have backed up”. I do not think that broadly applies (such as with individuals), but it certainly applies in most business contexts.
Obviously there's footguns in everything. Filesystem ones are just especially impactful.
But a lot of people out there will slap a bunch of USB 2.0 hard drives on top of an old gaming computer. I’m all for experimenting, and I sympathize that it’s expensive to run ZFS on “ZFS class” platforms and hardware. I don’t begrudge others that.
It would be really nice if there was something like ZFS that was a tad more flexibility and right in the kernel with consistent and concise user space tooling. Not everyone is comfortable with DKMS.
Can you provide some specifics? So far all I see is vague complains with no substance, and when complainers are lightly pressed they go defensive.
I did live specific situations over several years in a support engineer role where a double digit percentage of customers in enterprise configurations that ended up somewhere between terrible performance and catastrophic data loss due to the misunderstood configuration of a very complex piece of software.
If you wanna use ZFS, use ZFS. I'm not the internets crusader against it. I have no doubt there's thousands of PB out there of perfectly happy, well configured and healthy zpools. It has some truely next-gen features that are extremely useful. I've just seen it recommended so, so many times as a panacea when something simpler would be just as safe and long lasting.
It's kinda like using Kubernetes to run a few containers. Right?
I see.
> I did live specific situations over several years in a support engineer role where a double digit percentage of customers in enterprise configurations that ended up somewhere between terrible performance and catastrophic data loss due to the misunderstood configuration of a very complex piece of software.
I'm sorry, but this claim is outright unbelievable. If the project was even half as unstable as you claim to be, no one would ever use it in production at all. Either you are leaving out critical details such as non-standard patches and usages that have no relationship with real world usage, or you are fabricating tales.
Also, it's telling that no one stepped forward to offer any concrete details and specifics on these hypothetical issues. Makes you think.
I'm not being melodramatic. You can take a story or leave it. I'm not here to convince you one way or another.
And frankly I don't particularly appreciate being called a liar, btw. Nice use of quoting also. Good day.
There are workarounds, with their respective caveats and warnings.
The phrasing of this tends me to believe that the customers set up ZFS in a 'strange' (?) way. Or was this a bug(s) with-in ZFS itself?
Because when people talk about Btrfs issues, they are talking about the code itself and bugs that cause volumes to go AWOL and such.
(All file systems have foot-guns.)
There was a _very_ nasty bug in the ZFS L2ARC that took out a few PB at a couple of large installations. This was back in 2012/2013 when multiple PBs was very expensive. Was a case of ZFS putting data from the ARC into the pool after the ZIL/SLOG had been flushed.
Heck no native filesystem besides btrfs has compression, I'm saving HUNDREDS of GB with zstd compression on my machines with basically zero overhead
I've approached Kent two weeks ago and offered to help upstream changes into the kernel so he wouldn't have to interact with any of the kernel people ... he claimed without being able to explain why that having a go-between couldn't possibly help and that if he couldn't dictate the kernel release schedule he wouldn't want to ship the software anyway. And then proceeded to dunk on btrfs.
(Then maybe down the line people will realize Linus had a heart of gold behind his foul mouth.)
So, there are still behavioral issues here I take it? That is a bummer. This is not news to me, but I thought the situation has changed ever since.
From the past discussion, it's mainly grave behavioral issues but they also end up being technical. Such as trying to push new untested features into RCs and breaking builds, and resorting to flame wars to push these problematic patches forward instead of actually working them out with maintainers.
But yeah, the final straw was a very abusive email sent to a maintainer in the mailing list.
Seriously, every time I read tales about all the horrific things I've done in the kernel community, the stories grow and get wilder and wilder.
Oh wait.
It's you.
So even if you were right all along, the outcome is that people are screwed because bcachefs is no longer maintained in the kernel.
Every day, I ask myself, do I want to be right, or do I want to be effective?
That's how you end up with decisionmaking that's nothing more than popularity contests and no one even bothering to do the analysis on which option is technically better.
That way leads the death of leadership.
If you want to accomplish something as challenging as a filesystem, you do it by consistently making the right call and sticking to it, over and over and over.
And if you keep doing that, eventually you end up with the most active filesystem community around, and the ability to flip even the kernel community the bird when their weaponized incompetence becomes too much :)
So, the alternative is ZFS only, maybe HAMMER2. HAMMER2 does not look too bad either, except you need DragonflyBSD for that.
For how long have you been using it? Any issues? Any favorite feature(s) in particular?
Not perfect though. Performance at times doesn't seem better than just SSD, though I didn't really test that and I'm not sure if it's just hitting the HDD at those times. And there was a kernel version that didn't boot, though I'm staying on the bleeding edge with Arch Linux.
There's no inherent reason why a filesystem in userspace has to have a measurable performance impact over in-kernel, done right. It would be a lot of engineering work, though.
Context switches aren't that expensive when you're staying on the same core, it's IPIs (waking up a thread on another CPU) that's inherently expensive; and you need zero copy to/from the pagecache, which is tricky. But it totally could be done.
Modern Darwin is mostly a monolithic kernel, though more and more things are moving to userspace where possible (eg DriverKit).
One interesting side-effect of various spectre mitigations is silicon improving the performance of context switches. That has the side-effect of decreasing the cost of kernel/userspace transitions. It isn't nearly as expensive as people still believe - though it isn't free either.
This is what bcachefs is based on.
> You'll need make-bcache from the bcache-tools repository. Both the cache device and backing device must be formatted before use.
So, it's far from overlayfs. I could accept formatting the cache device, but not the backing storage.
I got partway thru setting up a script to copy recently accessed files from the HDD to the read-prioritized SSD.
My LLMs load up way faster, and I still have a source of truth volume in the huge HDD. It’s not something I’d use professionally though, way too janky.
Don't do RAID 5. Just don't. That's not just a btrfs shortcoming. I lost a hardware RAID 5 due to "puncture" which would have been fascinating to learn about if it hadn't happened to a production database. It's an academically interesting concept but it is too dangerous especially with how large drives are now, if you're buying three, buy four instead. RAID 10 is much safer especially for software RAID.
Stop parroting lies about btrfs. Since it became marked stable, it has been a reliable, trustworthy, performant filesystem.
But as much as I trust it I also have backups because if you love your data, it's your own fault if you don't back it up and regularly verify the backups.
In the last 10 years, btrfs:
1. Blew up three times on two unrelated systems due to internal bugs (one a desktop, one a server). Very few people were/are aware of the remount-only-once-in-degraded "FEATURE" where if a filesystem crashed, you could mount with -odegraded exactly only once, then the superblock would completely prevent mounting (error: invalid superblock). I'm not sure whether that's still the case or whether it got fixed (I hope so). By the way, these were on RAID1 arrays with 2 identical disks with metadata=dup and data=dup, so the filesystem was definitely mountable and usable. It basically killed the usecase of RAID1 for availability reasons. ZFS has allowed me to perform live data migrations while missing one or two disks across many reboots.
2. Developers merged patches to mainline, later released to stable, that completely broke discard=async (or something similar) which was a supported mount option from the manpages. My desktop SSD basically ate itself, had to restore from backups. IIRC the bug/mailing list discussions I found out later were along the lines of "nobody should be using it", so no impact.
3. Had (maybe still has - haven't checked) a bug where if you fill the whole disk, and then remove data, you can't rebalance, because the filesystem sees it has no more space available (all chunks are allocated). The trick I figured out was to shrink the filesystem to force data relocation, then re-expand it, then balance. It was ~5 years ago and I even wrote a blog post about it.
4. Quota tracking when using docker subvolumes is basically unusable due to the btrfs-cleaner "background" task (imagine VSCode + DevContainers taking 3m on a modern SSD to cleanup 1 big docker container). This is on 6.16.
5. Hit a random bug just 3 days ago on 6.16, where I was doing periodic rebalancing and removing a docker subvolume. 200+ lines of logs in dmesg, filesystem "corrupted" and remounted read-only. I was already sweating, not wanting to spend hours restoring from backups, but unexpectedly the filesystem mounted correctly after reboot. (first pleasant experience in years)
ZFS in 10y+ has basically only failed me when I had bad non-ECC RAM, period. Unfortunately I want the latest features for graphics etc on my desktop and ZFS being out of tree is a no-go. I also like to keep the same filesystem on desktop and server, so I can troubleshoot locally if required. So now I'm still on btrfs, but I was really banking on bcachefs.
Oh well, at least I won't have to wait >4 weeks for a version that I can compile with the latest stable kernel.
The only stable implementation is Synology's, the rest, even mainline stable, failed on me at least once in the last 10 years.
I had to disable quota tracking. It lags my whole desktop whenever that shit is running in the background. Makes it unusable on an interactive desktop.
Early bcachefs was ridiculously fast, it's gotten slower as we've grown all the features to compete with ZFS. All the database stuff that gives us amazing flexibility adds overhead (the btree iterator code has gotten fat), backpointers and modern accounting blew up our journalling overhead. A lot things that we needed for scalability, or hardening/self healing, have added overhead.
COW really isn't the main thing, it's cramming all the features in that we want these days while keeping the fastpaths fast that's the tricky part.
But, a lot of this stuff is fixable - performance just hasn't been the priority, since the actual users aren't complaining about performance and are instead clamoring for things like erasure coding.
(and, the performance numbers that I've seen comparing us to ZFS still put us _significantly faster)
????
> Don't do RAID 5.
Ah, OK, so not FUD
> Stop parroting lies about btrfs.
I seee
Claiming that anyone reporting problems is lying is acting in bad faith and makes your argument weaker.
Also, "works for me" isn't terribly convincing.
I've been in a similar situation, letting everyone know I was fired. Apparently in the US this has a negative connotation, and they use "being let go" (or something confusing as "handing in/being handed your 2 weeks notice", a concept completely unknown here). Here we only have one word for "your company terminating your employment", and there is no negative connotation associated with it. This can be difficult for non-natives. We can come across very weird or less intelligent.
> If the above offended anyone, I sincerely apology them.
Unless this was tongue-in-cheek, this kind of proves the point that language was the cause. The apology is a good move in any case.
The revised version, "Once the bcachefs maintainer conforms to the agreed process and the code is maintained upstream again" is still lecturing and piling on, as the LWN comments say:
https://lwn.net/Articles/1037496/
It is the classic case of CoC people and their inner circle denouncing someone, and subsequently the entire Internet keeps piling on the target.
I don't like politics in my repo as much as the next guy, but this case is pretty clear cut. There's no ambiguity or controversy.
How cynical. It's the kernel maintainer, not the bcachefs maintainer, who does not behave and has a huge history of unprofessional behavior for decades.
it is not like he was not explicitly warned.
Bug fix windows are for bug fix. If it’s not a bug fix, it goes in the next version. That’s how the kernel release cycle works. It’s not very complicated.
If it’s so unstable that it urgently needs new features shipped regularly, I think it’s entirely legitimate that it has to live out of tree until it’s actually stable enough.
https://lwn.net/ml/all/bece61a0-b818-4d59-b340-860e94080f0d@...
The ever escalating drama and cynicism in the reactions this stuff gets though... bloody hell, what is with people these days?
https://lkml.org/lkml/2013/7/15/374
That is a reasonable compromise. Except when someone actually snaps back at him.
Human nature is wicked.
I'm quite happy to be forging my own path now.