There’s been some Friday night kernel drama on the Linux kernel mailing list… Linus Torvalds has expressed regrets for merging the Bcachefs file-system and an ensuing back-and-forth between the file-system maintainer.
Kent developed for like 10 years on his own. He’s just having a hard time learning how to play with others, and deal with large priority cycles. He just needs to know that sometime his changes will get pushed to the next cycle.
This. Well said.
Kent is reasonable, and sees Linus’s need to keep order. I think he just pushes it sometimes, and doesn’t understand how problematic that can be.
That said - he has resubmitted an amended version of the patch, that doesn’t touch code outside of bcachefs, and is less than 1/3 the size.
Can someone say why bcachefs is interesting? Btrfs I can sort of understand. I haven’t much kept track of most others.
bcachefs is way more flexible than btrfs on multi-device filesystems. You can group storage devices together based on performance/capacity/whatever else, and then do funky things like assigning a group of SSDs as a write-through/write-back cache for a bigger array of HDDs. You can also configure a ton of properties for individual files or directories, including the cache+main storage group, amount of data replicas, compression type, and quite a bit more.
So you could have two files in the same folder, one of them stored compressed on an array of HDDs in RAID10 and the other one stored on a different array of HDDs uncompressed in RAID5 with a write-back SSD cache, and wouldn’t have to fiddle around with multiple filesystems and bind mounts - everything can be configured by simply setting xattr values. You could even have a third file which is striped across both groups of HDDs without having to partition them up.
Thank you. w o w
two files in the same folder, one of them stored compressed on an array of HDDs in RAID10 and the other one stored on a different array […]
Now that’s what I call serious over-engineering.
Who in the world wants to use that?
And does that developer maybe have some spare time? /s
This is actually a feature that enterprise SAN solutions have had for a while, being able choose your level of redundancy & performance at a file level is extremely useful for minimising downtime and not replicating ephemeral data.
Most filesystem features are not for the average user who has their data replicated in a cloud service; they’re for businesses where this flexibility saves a lot of money.
I’ll also tac on that when you use cloud storage, what do you think your stuff is stored on at the end of the day? Sure as shit not Bcachefs yet, but it’s more likely than not on some netapp appliance for the same features that Bcachefs is developing.
This probably meets some extreme corporate usecase where they are serving millions of customers.
It’s not that obscure - I had a use case a while back where I had multiple rocksdb instances running on the same machine and wanted each of them to store their WAL only on SSD storage with compression and have the main tables be stored uncompressed on an HDD array with write-through SSD cache (ideally using the same set of SSDs for cost). I eventually did it, but it required partitioning the SSDs in half, using one half for a bcache (not bcachefs) in front of the HDDs and then using the other half of the SSDs to create a compressed filesystem which I then created subdirectories on and bind mounted each into the corresponding rocksdb database.
Yes, it works, but it’s also ugly as sin and the SSD allocation between the cache and the WAL storage is also fixed (I’d like to use as much space as possible for caching). This would be just a few simple commands using bcachefs, and would also be completely transparent once configured (no messing around with dozens of fstab entries or bind mounts).
My company serves millions, too. We don’t have such needs.
Congrats.
bcachefs is meant to be more reliable than btrfs - which has had issues with since it was released (especially in the early days). Though bcachefs has yet to be proven at scale that it can beat btrfs at that.
Bcachefs also supports more features I believe - like encryption. No need for an extra layer below the filesystem to get the benefits of encryption. Much like compression that also happens on both btrfs and bcachefs.
Btrfs also has issues with certain raid configurations, I don’t think it yet has support for raid 5/6 like setup and it has promised that for - um, well maybe a decade already? and I still have not heard any signs of it making any progress on that front. Though bcachefs also still has this on their wishlist - but I see more hope for them getting it before btrfs which seems to have given up on that feature.
Bcachefs also claims to have a cleaner codebase than btrfs.
Though bcachefs is still very new so we will see how true some of its claims will end up being. But if true it does seem like the more interesting filesystem overall.
Also because it’s meant to be an enterprise level filesystem like ZFS, but without the licensing baggage. They share a lot of feature sets.
In addition to the comment on the mentioned better hardware flexibility, I’ve seen really interesting features like defining compression & deduplication in a granular way, even to the point of having a compression algo when you first write data, and then a different more expensive one when your computer is idle.
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Bruh, you can’t just submit entirely new data structures as “fixes”, let alone past the merge window.
It should not be hard at all to grasp that.
He accepted Linus’s needs as the project head to keep order. He resubmitted the patch set without the contentious parts. It’s less than 1/3 the size and doesn’t touch code outside of bcachefs. Problem solved.
Honestly, Kent seems pretty reasonable (though impassioned), and bcachefs well probably make it, and Kent will get used to just submitting things at the right time in the cycle.
I was interested in bcachefs years ago, but Kent seems to keep shooting himself in the foot when it comes to getting any traction with it.
It’s not as bad as it seems. He just doesn’t know how valuable working with the provided structure is yet. A lot of innovative thinkers are used to questioning, bending, and tinkering with the rules. He’s just still learning how necessary the existing structure is.
Was considering bcachefs at some point but after seeing this, definitely a no for the foreseeable future. I don’t like surprises in my file systems.
I definitely feel bcachefs is much more practical than zfs for home storage, I’ve used both. I don’t use zfs unless it’s TrueNAS because of the licensing issues, but bcachefs solves all of that and you can use different sized drives. I look forward to it being stable and glad it’s working out. Luckily the only side affect is Linus’ regretfulness. 😂
Use ext4. It just works.
ext4 is intended for a completely different use case, though? bcachefs is competing with btrfs and ZFS in big storage arrays spanning multiple drives, probably with SSD cache. ext4 is a nice filesystem for client devices, but doesn’t support some things which are kinda fundamental at larger scales like data checksumming, snapshots, or transparent compression.
There’s XFS for larger scale stuff.
XFS still isn’t a multi-device filesystem, though… of course you can run it on top of mdraid/LVM, but that still doesn’t come close to the flexibility of what these specialized filesystems can do. Being able to simply run
btrfs device add /dev/sdx1 /and immediately having the new space available is far less hassle than adding a device to an md array, then resizing the partition and then resizing the filesystem (and removing a device is even worse). Snapshots are a similar deal - sure, LVM can let you snapshot your entire virtual block device, but your snapshots are block devices themselves which need to be explicitly mounted, while in btrfs/bcachefs a snapshot is just a directory, and can be isolated to a specific subvolume rather than the entire block device.Data checksums are also substantially less useful when the filesystem can’t address the underlying devices individually, because it makes repairing the data from a replica impossible. If you have a file on an md RAID1 device and one of the replicas has a bad block, you might be able to detect the bitrot by verifying the checksum, but you can’t actually fix it, because even though there is a second copy of the data on another drive, mdadm simply exposes a simple block device and doesn’t provide any way to read from “the other copy”. mdraid can recover from total drive failure, but not data corruption.
You might as well say use fat32 it just works.
Not really. It has a quite small file size limit afaik.
Like there’s not a bunch of stuff EXT 4 can’t do that BTRFS and whatever this other acronym soup can do.
It’s the entire point of my post. E x t 4 does work but it doesn’t do the stuff these other file systems do so they are an advantageous choice for some things.
One point: ext4 has a maximum file size of 16TiB. To a regular user that is stupidly huge and of no concern but it’s exactly the type of thing you overlook if you “just use ext4” on anything and everything then end up with your database broken at work because of said bad advice.
Use the filesystem that makes the most sense for your use case. Consider it every single time you format a disk. Don’t become complacent! Also fuck around with the new shit from time to time! I decided to format my Linux desktop partitions with btrfs over a decade ago and as a result I’m an excellent user of that filesystem but you know what? I’m thinking I’ll try bcachefs soon and fiddle around more with my zfs partition on my HTPC.
BTW: If you’re thinking about trying out btrfs I would encourage you to learn about it’s non-trivial maintenance tasks. btrfs needs you to fuck with it from time to time or you’ll run out of disk space “for no reason”. You can schedule cron jobs to take care of everything (as I have done) but you still need to learn how it all works. It’s not a “set it and forget it” FS like ext4.
I have 52 terabytes of BTRFS, I’ve been on it for about 5 years.
I think we’re just talking about different priorities. For me stability is the most important in production. For you features seem to matter more. For me it’s enough if a file system can store, write, read and not lose files. I guess it depends on what the use case and the budget are.
Yeah, some people have needs that you don’t have. That’s why I commented on your blanket statement of just use EXT4.
I have BTRFS in production all over the place. Snapshots are extremely useful for what I do.
and not lose files
Which is exactly why you’d want to run a CoW filesystem with redundancy.
ext4 aims to not lose data under the assumption that the single underlying drive is reliable. btrfs/bcachefs/ZFS assume that one/many of the perhaps dozens of underlying drives could fail entirely or start returning garbage at any time, and try to ensure that the bad drive can be kicked out and replaced without losing any data or interrupting the system. They’re both aiming for stability, but stability requirements are much different at scale than a “dumb” filesystem can offer, because once you have enough drives one of them WILL fail and ext4 cannot save you in that situation.
Complaining that datacenter-grade filesystems are unreliable when using them in your home computer is like removing all but one of the engines from a 747 and then complaining that it’s prone to crashing. Of course it is, because it was designed under the assumption that there would be redundancy.
No. You can layer ext4 with LVM and LUKS to get a lot of features (but not all) that you get with BTRFS or ZFS. FAT is not suitable for anything other than legacy stuff.
My point is there are features that you don’t get in EXT that are completely reasonable to use and workflows.
When someone says just use EXT4, they’re just missing the fact that people may want or need those other features.
Your response to FAT is exactly my point.
Torvalds rejected the merge, and that’s pretty much what he said - no one is using bcachefs.
There’s no reason for a “fix” to be 1k+ lines, these sorts of changes need to come earlier in the release cycle.
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You had corruption with btrfs? Was this with a spinning disk or an SSD?
I’ve been using btrfs for over a decade on several filesystems/machines and I’ve had my share of problems (mostly due to ignorance) but I’ve never encountered corruption. Mostly I just run out of disk space because I forgot to balance or the disk itself had an issue and I lost whatever it was that was stored in those blocks.
I’ve had to repair a btrfs partition before due to who-knows-what back when it was new but it’s been over a decade since I’ve had an issue like that. I remember
btrfs check --repairbeing totally useless back then haha. My memory on that event is fuzzy but I think I fixed whatever it was bitching about by remounting the filesystem with an extra option that forced it to recreate a cache of some sort. It ran for many years after that until the disk spun itself into oblivion.
