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What's with all these hip filesystems and how are they different?
(lm.paradisus.day)
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this post was submitted on 07 Dec 2023
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As with every software/product: they have different features.
ZFS is not really hip. It's pretty old. But also pretty solid. Unfortunately it's licensed in a way that is maybe incompatible with the GPL, so no one wants to take the risk of trying to get it into Linux. So in the Linux world it is always a third-party-addon. In the BSD or Solaris world though ....
btrfs has similar goals as ZFS (more to that soon) but has been developed right inside the kernel all along, so it typically works out of the box. It has a bit of a complicated history with it's stability/reliability from which it still suffers (the history, not the stability). Many/most people run it with zero problems, some will still cite problems they had in the past, some apparently also still have problems.
bcachefs is also looming around the corner and might tackle problems differently, bringing us all the nice features with less bugs (optimism, yay). But it's an even younger FS than btrfs, so only time will tell.
ext4 is an iteration on ext3 on ext2. So it's pretty fucking stable and heavily battle tested.
Now why even care? ZFS, btrfs and bcachefs are filesystems following the COW philisophy (copy on write), meaning you might lose a bit performance but win on reliability. It also allows easily enabling snapshots, which all three bring you out of the box. So you can basically say "mark the current state of the filesystem with tag/label/whatever 'x'" and every subsequent changes (since they are copies) will not touch the old snapshots, allowing you to easily roll back a whole partition. (Of course that takes up space, but only incrementally.)
They also bring native support for different RAID levels making additional layers like mdadm unnecessary. In case of ZFS and bcachefs, you also have native encryption, making LUKS obsolete.
For typical desktop use: ext4 is totally fine. Snapshots are extremely convenient if something breaks and you can basically revert the changes back in a single command. They don't replace a backup strategy, so in the end you should have some data security measures in place anyway.
*Edit: forgot a word.
Perhaps I'm guilty of good luck, but is the trade off of performance for reliability worth it? How often is reliability a problem?
As a different use case altogether, suppose I was setting up a NAS over a couple drives. Does choosing something with COW have anything to do with redundancy?
Maybe my question is, are there applications where zfs/btrfs is more or less appropriate than ext4 or even FAT?
For fileservers ZFS (and by extension btrfs) have a clear advantage. The main thing is, that you can relatively easily extend and section off storage pools. For ext4 you would need LVM to somewhat achieve something similar, but it's still not as mighty as what ZFS (and btrfs) offer out of the box.
ZFS also has a lot of caching strategies specifically optimized for storage boxes. Means: it will eat your RAM, but become pretty fast. That's not a trade-off you want on a desktop (or a multi purpose server), since you typically also need RAM for applications running. But on a NAS, that is completely fine. AFAIK TrueNAS defaults to ZFS. Synology uses btrfs by default. Proxmox runs on ZFS.
ZFS cache will mark itself as such, so if the kernel needs more RAM for applications it can just dump some of the ZFS cache and use whatever it needs.
I see lots of threads on homelab where new users are like “HELP MY ZFS IS USING 100% MEMORY” and we have to talk them off that ledge: unused RAM is wasted RAM, ZFS is making sure you’re running fast AF.
In theory. Practically unless I limit the max ARC size, processes get OOM killed quite frequently here.
In theory. But how it is implemented in current systems, reserved memory can not be used by other processes and those other processes can not just ask the hog to give some space. Eventually, the hog gets OOM-killed or the system freezes.
Even when, as the comment says, the memory is marked as cache?
Windows doesn't have this problem
Neither of them likes to deal with very low amounts of free space, so don't use it on places where that is often a scarcity. ZFS gets really slow when free space is almost none, and nowadays I don't know about BTRFS but a few years ago filling the partition caused data corruption there.