Liam Proven(Written by Reg staff) Silver badge
Reply Icon
Re: Justice for bcachefs!

Anyone want to educate me on what bcachefs brings to the party that, say, ext4 doesn't?

I have gone into this at some length before. For instance, here:

https://www.theregister.com/2022/03/18/bcachefs/

... which is linked from the article you are commenting upon.

ext2/3/4 only handle one partition on one disk at a time.

As well as this, first, for partitioning, you need another tool, such as MBR or GPT. But you can do without, in some situations.

For RAID, you need another tool, e.g. kernel mdraid.

(Example of the intersection of 1 & 2: it is normal to make a new device with mdraid and then format that new device directly with ext4, not partitioning it first.)

Want resizable volumes, which might span multiple disks? You need another tool, LVM2.

But don't try to manage mdraid volumes with LVM2, or LVM2 with mdraid. Doesn't work.

Want encryption? You need another tool, such as LUKS. There are several.

Watch out if you use hardware RAID or hardware encryption. The existing tools won't see it or handle it.

It is complicated. There is lots of room for error.

So, ZFS fixed that. It does the partitioning part, and the RAID part, and the encryption part, and the resizing part, and also the mounting part, all in one.

It's great, it's easier and it's faster and you can nominate a fast disk to act as a cache for a bigger array of slower disks...

And it can take snapshots. While it is running. Take an image of your whole OS in a millisecond and then keep running and all the changes go somewhere new. So you can do an entire distribution upgrade, realise one critical tool doesn't work on the new version, and undo the entire thing, and go back to where you were...

While keeping all your data and all your files intact.

All while the OS is running.

And it does it all in one tool.

But it's not GPL so it can't be built into the Linux kernel.

You can load it as a module and that's fine but its cache remains separate from the Linux cache, so it uses twice the memory, maybe more.

So, there are other GPL tools that replicate some of this.

Btrfs does some of it. But Btrfs overlaps with, and does not interoperate with, LVM and with mdraid and with LUKS... and it collapses if the disk fills up... and it's easy to fill up because its "how much free space do I have?" command is broken and lies... and when it corrupts, you can't fix it.

It is, in short, crap, but you can't say that because it is rude and so being the way of Linux it has passionate defenders who complain they are being attacked if you mention problems.

Bcachefs is an attempt to fix this with an all-GPL tool, designed for Linux, which does all the nice stuff ZFS does but integrates better with the Linux kernel. It does not just replace ext4, it will let you replace ext4 and LVM2 and LUKS and mdraid, all in one tool.

It will do everything Btrfs does but not collapse in a heap if the volume fills up. And if it does have problems, you can fix it.

All this is good. All this is needed. We know it's doable because it already exists in a tool from Solaris in a form that FreeBSD can use but Linux can't.

But in a mean-spirited and unfair summary, Kent Overstreet is young and smart and cocky and wants to deliver something better for Linux and Linux users, and the old guard hate that and they hate him. They hate that this smart punk kid has shown up the problems with their tools they've been working on for 20-30 years.