Bcachefs Goes to "Externally Maintained"

94 ksec 68 8/30/2025, 1:07:41 PM lwn.net ↗

Comments (68)

uecker · 23m ago
Who would use a file system which essentially seems to be developed by a single person? A bus-factor of one seems unacceptable for a FS. But maybe I am wrong and there are other developers, then why do they not take over upstreaming if the main developer is unable to collaborate with the kernel community.
betaby · 2h ago
The sad part, that despite the years of the development BTRS never reached the parity with ZFS. And yesterday's news "Josef Bacik who is a long-time Btrfs developer and active co-maintainer alongside David Sterba is leaving Meta. Additionally, he's also stepping back from Linux kernel development as his primary job." see https://www.phoronix.com/news/Josef-Bacik-Leaves-Meta

There is no 'modern' ZFS-like fs in Linux nowadays.

ibgeek · 2h ago
This isn’t BTRFS
doubletwoyou · 1h ago
This might not be directly about btrfs but bcachefs zfs and btrfs are the only filesystems for Linux that provide modern features like transparent compression, snapshots, and CoW.

zfs is out of tree leaving it as an unviable option for many people. This news means that bcachefs is going to be in a very weird state in-kernel, which leaves only btrfs as the only other in-tree ‘modern’ filesystem.

This news about bcachefs has ramifications about the state of ‘modern’ FSes in Linux, and I’d say this news about the btrfs maintainer taking a step back is related to this.

ajross · 1h ago
Meh. This war was stale like nine years ago. At this point the originally-beaten horse has decomposed into soil. My general reply to this is:

1. The dm layer gives you cow/snapshots for any filesystem you want already and has for more than a decade. Some implementations actually use it for clever trickery like updates, even. Anyone who has software requirements in this space (as distinct from "wants to yell on the internet about it") is very well served.

2. Compression seems silly in the modern world. Virtually everything is already compressed. To first approximation, every byte in persistent storage anywhere in the world is in a lossy media format. And the ones that aren't are in some other cooked format. The only workloads where you see significant use of losslessly-compressible data are in situations (databases) where you have app-managed storage performance (and who see little value from filesystem choice) or ones (software building, data science, ML training) where there's lots of ephemeral intermediate files being produced. And again those are usages where fancy filesystems are poorly deployed, you're going to throw it all away within hours to days anyway.

Filesystems are a solved problem. If ZFS disappeared from the world today... really who would even care? Only those of us still around trying to shout on the internet.

fluidcruft · 27m ago
One feature I like about ZFS and have not seen elsewhere is that you can have each filesystem within the pool use its own encryption keys but more importantly all of the pool's data integrity and maintenance protection (scrubs, migrations, etc) work with filesystems in their encrypted state. So you can boot up the full system and then unlock and access projects only as needed.

The dm stuff is one key for the entire partition and you can't check it for bitrot or repair it without the key.

doubletwoyou · 1h ago
I know my own personal anecdote isn’t much, but I’ve noticed pretty good space savings on the order of like 100 GB from zstd compression and CoW on my personal disks with btrfs

As for the snapshots, things like LVM snapshots are pretty coarse, especially for someone like me where I run dm-crypt on top of LVM

I’d say zfs would be pretty well missed with its data integrity features. I’ve heard that btrfs is worse in that aspect, so given that btrfs saved my bacon with a dying ssd, I can only imagine what zfs does.

anon-3988 · 1h ago
> Filesystems are a solved problem. If ZFS disappeared from the world today... really who would even care? Only those of us still around trying to shout on the internet.

Yeah nah, have you tried processing terabytes of data every day and storing them? It gets better now with DDR5 but bit flips do actually happen.

ajross · 37m ago
And once more, you're positing the lack of a feature that is available and very robust (c.f. "yell on the internet" vs. "discuss solutions to a problem"). You don't need your filesystem to integrate checksumming when dm/lvm already do it for you.
bombcar · 1h ago
Bit flips can happen, and if it’s a problem you should have additional verification above the filesystem layer, even if using ZFS.

And maybe below it.

And backups.

Backups make a lot of this minor.

toast0 · 54m ago
Backups are great, but don't help much if you backup corrupted data.

You can certainly add verification above and below your filesystem, but the filesystem seems like a good layer to have verification. Capturing a checksum while writing and verifying it while reading seems appropriate; zfs scrub is a convenient way to check everything on a regular basis. Personally, my data feels important enough to make that level of effort, but not important enough to do anything else.

ajross · 18m ago
FWIW, framed the way you do, I'd say the block device layer would be an *even better* place for that validation, no?

> Personally, my data feels important enough to make that level of effort, but not important enough to do anything else.

OMG. Backups! You need backups! Worry about polishing your geek cred once your data is on physically separate storage. Seriously, this is not a technology choice problem. Go to Amazon and buy an exfat stick, whatever. By far the most important thing you're ever going to do for your data is Back. It. Up.

Filesystem choice is, and I repeat, very much a yell-on-the-internet kind of thing. It makes you feel smart on HN. Backups to junky Chinese flash sticks are what are going to save you from losing data.

pdimitar · 1h ago
> The dm layer gives you cow/snapshots for any filesystem you want already and has for more than a decade. Some implementations actually use it for clever trickery like updates, even.

O_o

Apparently I've been living under a rock, can you please show us a link about this? I was just recently (casually) looking into bolting ZFS/BTRFS-like partial snapshot features to simulate my own atomic distro where I am able to freely roll back if an update goes bad. Think Linux's Timeshift with something little extra.

tux3 · 1h ago
There are downsides to adding features in layers, as opposed to integrating them with the FS, but dm can do quite a lot:

https://docs.kernel.org/admin-guide/device-mapper/snapshot.h...

zozbot234 · 1h ago
Does btrfs still eat your data if you try to use its included RAID featureset? Does it still break in a major way if you're close to running out of disk space? What I'm seeing is that most major Linux distributions still default to non-btrfs options for their default install, generally ext4.
skibbityboop · 47m ago
Anecdotal but btrfs is the only filesystem I've lost data with (and it wasn't in a RAID configuration). That combined with the btrfs tools being the most aggressively bad management utilities out there* ensure that I'm staying with ext4/xfs/zfs for now.

*Coming from the extremely well thought out and documented zfs utilities to btrfs will have you wondering wtf fairly frequently while you learn your way around.

NewJazz · 2h ago
Btrfs is the closest in-tree bcachefs alternative.
ofrzeta · 2h ago
Suse Linux Enterprise still uses Btrfs as the Root-FS, so it can't be that bad, right? What is Chris Mason actually doing these days? I did some googling and only found out that he was working on a tool called "rsched".
dmm · 30m ago
btrfs is fine for single disks or mirrors. In my experience, the main advantages of zfs over btrfs is that ZFS has production ready raid5/6 like parity modes and has much better performance for small sync writes, which are common for databases and hosting VM images.
tarruda · 1h ago
Since the existing bcachefs driver will not be removed, and the problem is the bcachefs developer not following the rules, I wonder if someone else could take on the role of pulling bcachefs changes into the mainline, while also following the merge window rules.
Volundr · 3h ago
Damn. I was enjoying not having to deal with the fun of ZFS and DKMS, but it seems like now bcachefs will be in the same boat, either dealing with DKMS and occasional breakage or sticking with the kernel version that slowly gets more and more out of date.
WD-42 · 2h ago
The article says that bcachefs is not being removed from the mainline kernel. This looks like mostly a workaround for Linus and other kernel devs to not have to deal with Kent directly.
ffsm8 · 1h ago
The three listed options in the OP thread were

* Another kernel Dev takes over management and they tread it as a fork (highly unlikely according to their estimate)

* Kent hires someone to upstream the changes for him and Kent stops complaining wrt when it's getting merged

* Bcachefs gets no maintenance and will likely be removed in the next major release

I do not know him personally, but most interactions I've read online by him sounded grounded and not particularly offensive, so I'm abstaining from making any kind of judgement on it.

But while I have no stake in this, Drama really does seem to follow Kent around for one reason or another. And it's never his fault if you take him by his public statements - which I want to repeat: he sounds very grounded and not offensive to me whatsoever.

sarlalian · 24m ago
If you look at all the places where Kent has had drama, the common element is him and environments that have pretty rigid workflows. The common thread seems to be him not respecting workflows and processes that those places have, that inconvenience his goals. So, he ignores the workflows and processes of those places, and creates a constant state of friction and papercuts for those who he needs to accomplish his goals. They eventually get fed up, and either say no, not working with you anymore, or no, you’re not welcome to contribute here anymore.

He’s not super offensive, but he will tell a Debian package maintainer that their process sucks, and the should change it and they are being stupid by following that process. Overall, he seems a bit entitled, and unwilling to compromise with others. It’s not just Kent though, the areas that seem to be the most problematic for him, are when it’s an unstoppable force (Kent), and an immovable wall (Linux / Debian).

Working in the Linux kernel is well known for its frustrations and the personal conflict that it creates, to the point that there are almost no linux kernel devs/maintainers that aren’t paid to do the work. You can see a similar set of events happen with Rust4Linux people, Asahi linux project and their R4L drivers, etc.

tux3 · 1h ago
It's complicated, no one really knows what "externally maintained" entails at the moment. Linus is not exactly poised to pull directly from Kent, and there is no solution lined-up at the moment.

Both Linus and Kent drive a hard bargain, and it's not as simple as finding someone else to blindly forward bcachefs patches. At the first sign of conflict, the poor person in the middle would have no power, no way to make anyone back down, and we'd be back to square one.

It's in limbo, and there is still time, but if left to bitrot it will be removed eventually.

immibis · 56m ago
That person would be accountable to Linus, but not to Kent
tux3 · 44m ago
Unfortunately, there's also nothing they can do if Kent says no. Say there's a disagreement on a patch that touches something outside fs/bcachefs, that person can't exactly write their own patches incorporating the feedback. They're not going to fork and maintain their own patches. They'd be stuck between a rock and a hard place, and that gets us back to a deadlock.

The issue is that I have never seen Kent back down a single time. Kent will explain in details why the rules are bullshit and don't apply in this particular case, every single time, without any room for compromise.

If the only problem was when to send patches, that would be one thing. But disagreements over patches aren't just a timing problem that can be routed around.

NewJazz · 2h ago
FWIW DKMS is not the only way to distribute out of tree modules.

https://github.com/chimera-linux/ckms

mustache_kimono · 2h ago
> Damn. I was enjoying not having to deal with the fun of ZFS and DKMS, but it seems like now bcachefs will be in the same boat, either dealing with DKMS and occasional breakage or sticking with the kernel version that slowly gets more and more out of date.

Your distro could very easily include bcachefs if it wishes? Although I think the ZFS + Linux situation is mostly Linux religiosity gone wild, that very particular problem doesn't exist re: bcachefs?

The problem with bcachefs is the problem with btrfs. It mostly still doesn't work to solve the problems ZFS already solves.

kstrauser · 2h ago
> Although I think the ZFS + Linux situation is mostly Linux religiosity gone wild

I can think of non-religious reasons to want to avoid legal fights with Oracle.

jchw · 1h ago
> Although I think the ZFS + Linux situation is mostly Linux religiosity gone wild,

I think the Linux Kernel just doesn't want to be potentially in violation of Oracle's copyrights. That really doesn't seem that unreasonable to me, even if it feels pointless to you.

LeoPanthera · 2h ago
It's orphaned in Debian as well, but I'm not sure what significant advantages it has over btrfs, which is very stable these days.
betaby · 2h ago
btrfs was unusable in multi disk setup for kernels 6.1 and older. Didn't try since then. How's stable btrs today in such setups?

Also see https://www.phoronix.com/news/Josef-Bacik-Leaves-Meta

LeoPanthera · 2h ago
It's sort of frustrating that this constantly comes up. It's true that btrfs does have issues with RAID-5 and RAID-6 configurations, but this is frequently used (not necessarily by you) as some kind of gotcha as to why you shouldn't use it at all. That's insane. I promise that disk spanning issues won't affect your use of it on your tiny ThinkPad SSD.

It's important to note that striping and mirroring works just fine. It's only the 5/6 modes that are unstable: https://btrfs.readthedocs.io/en/stable/Status.html#block-gro...

betaby · 2h ago
But RAID-6 is the closest approximation to raid-z2 from ZFS! And raid-z2 is stable for a decade+. Indeed btrfs works just fine on my laptop. My point is that Linux lacks ZFS-like fs for large multi disc setups.
NewJazz · 2h ago
Seriously for the people who take filesystems seriously and have strong preferences... Multi disk might be important.
wtallis · 38m ago
BTRFS does have stable, usable multi-disk support. The RAID 0, 1, and 10 modes are fine. I've been using BTRFS RAID1 for over a decade and across numerous disk failures. It's by far the best solution for building a durable array on my home server stuffed full of a random assortment of disks—ZFS will never have the flexibility to be useful with mismatched capacities like this. It's only the parity RAID modes that BTRFS lacks, and that's a real disadvantage but is hardly the whole story.
AaronFriel · 2h ago
Respectfully to the maintainers:

How can this be a stable filesystem if parity is unstable and risks data loss?

How has this been allowed to happen?

It just seems so profoundly unserious to me.

wtallis · 37m ago
Does the whole filesystem need to be marked as unstable if it has a single experimental feature? Is any other filesystem held to that standard?
risho · 1h ago
as it turns out raid 5 and 6 being broken is kind of a big deal for people. its also far from ideal that the filesystem has random landmines that you can accidentally step on if you don't happen to read hacker news every day.
__turbobrew__ · 2h ago
How can I know what configurations of btrfs lose my data?

I also have had to deal with thousands of nodes kernel panicing due to a btrfs bug in linux kernel 6.8 (stable ubuntu release).

ffsm8 · 1h ago
I thought the usual recommendation was to use mdadm to build the disk pool and then use btrfs on top of that - but that might be out of date. I haven't used it in a while
rendaw · 2h ago
> on your tiny ThinkPad SSD

Ad hominem. My thinkpad ssd is massive.

LeoPanthera · 2h ago
Good news, it will work just fine on that too.
turtletontine · 1h ago
I’ve been running btrfs on a little home Debian NAS for over a year now. I have no complaints - it’s been working smoothly, doing exactly what I want. I have a heterogeneous set of probably 6 discs, >20TB total, no problems.

*caveat: I’m using RAID 10, not a parity RAID. It could have problems with parity RAID. So? If you really really want RAID 5, then just use md to make your RAID 5 device and put btrfs on top.

deknos · 1h ago
i run btrfs on servers and desktops. it's usuable.
williamstein · 1h ago
So do I and BTRFS is extremely good these days. It's also much faster than ZFS at mounting a disk with a large number of filesystems (=subvolumes), which is critical for building certain types of fileservers at scale. In contrast, ZFS scales horribly as the number of filesystems increases, where btrfs seems to be O(1). btrfs's quota functionality is also much better than it used to be (and very flexible), after all the work Meta put into it. Finally, having the option of easy writable snapshots is nice. BTRFS is fantastic!
cmurf · 2h ago
Absurd to claim it’s unusable without any qualification whatsoever.

Single, dup, raid0, raid1, raid10 have been usable and stable for a decade or more.

omoikane · 2h ago
Related: Linux CoC Announces Decision Wrt Kent Overstreet (Bcachefs) (kernel.org)

https://news.ycombinator.com/item?id=42221564 - 2024-11-23, 103 comments

NewJazz · 2h ago
FreeBSD is giving me a sultry look as I ponder my NAS build.
kstrauser · 1h ago
I'm in that boat. I'm looking over at that Synology unit sitting in the corner of my living room, knowing it'll be the last of its kind to live here, and wondering what its replacement will look like. FreeBSD's been good to me and it might be time to reintroduce myself to it.
bpye · 49m ago
There are some Linux distros with ZFS as a near first class citizen. NixOS is one, I believe Alpine is another.
mrighele · 3m ago
Ubuntu too.
_0xdd · 1h ago
Go for it. I made the switch ~10 years ago and didn't regret it at all. First-class, rock solid ZFS integration. Saved my data on more than one occasion.
sevg · 2h ago
Is it just me or does Kent seem self-destructively glued to his own idea of how kernel development should work?

I don’t doubt that people on all sides have made mis-steps, but from the outside it mostly just seems like Kent doesn’t want to play by the rules (despite having been given years of patience).

toast0 · 1h ago
It's not just kernel development. In the lwn thread, he mentioned and then demonstrated difficulty working with Debian developers as well.

IMHO, what his communications show is an unwillingness to acknowledge that other projects that include his work have focus, priorities, and policies that are not the same as that of his project. Also, expecting exceptions to be made for his case, since exceptions have been made in other cases.

Again IMHO, I think he would be better off developing apart with an announcement mailing list. When urgent changes are made, send to the announcement list. Let other interested parties sort out the process of getting those changes into the kernel and distributions.

If people come with bug reports from old versions distributed by others, let them know how to get the most up to date version from his repository, and maybe gently poke the distributors.

Yes, that means users will have older versions and not get fixes immediately. But what he's doing isn't working to get fixes to users immediately either.

bornfreddy · 31m ago
Being an outsider to this whole scene, the whole thread reads very differently to me.

Kent seems very patient in explaining his position (and frustrations arising from other people introducing bugs to his code) and the kernel & debian folks are performing a smearing campaign instead of replying to what I see are genuine problems in the process. As an example, the quotes that are referenced by user paravoid are, imho, taken out of context (judging by reading the provided links).

There probably is a lot more history to it, but judging from that thread it's not Kent who looks like a bad guy.

ajb · 44m ago
I think Kent is in the wrong here, but it really doesn't help that the kernel people from Linus on down are seemingly unable to explain the problem, and instead resort to playground insults. Apart from being unprofessional and making for a hostile work environment, it doesn't really communicate why Kent's actions are problematic, so I've some sympathy for his not believing that they are.
arp242 · 2m ago
People have explaining things, at great length, many times. Many of these have been posted to HN before, either as submissions or comments.

Kent just does not listen. Every time the discussion starts from the top. Even if you do agree on some compromise, in a month or two he'll just do the same thing again and all the same arguments start again.

You can't expect people to detail about four or five years of context in every single engagement for the benefit of interested 3rd parties like you or me.

sevg · 34m ago
> it doesn't really communicate why Kent's actions are problematic

I agree that the kernel community can be a hostile environment.

Though I’d argue that people _have_ tried to explain things to Kent, multiple times. At least a few have been calm, respectful attempts.

Sadly, Kent responds to everything in an email except the key part that is being pointed out to him (usually his behavior). Or deflects by going on the attack. And generally refuses to apologise.

ajb · 7m ago
Definitely not saying that the problems are all on one side here. Agreed that going on the attack was bad (as well as dumb).

I just think that while, yes, the kernel folks have tried to explain, they didn't explain well. The "why" of it is a people thing. Linus needs to be able to trust that people he's delegated some authority will respect its limits. The maintainers need to be able to trust that each other maintainer will respect the area that they have been delegated authority over. I think that Kent genuinely doesn't get this.

yxhuvud · 16m ago
I've seen plenty of times where the problems has been explained to Kent. But he just don't give a shit about the problems of people that isn't himself or that doesn't use his file system experiences.
rstat1 · 2h ago
Surprised it took this long.