Examining btrfs, Linux’s perpetually half-finished filesystem

guest · Sep 24, 2021

Examining btrfs, Linux’s perpetually half-finished filesystem
This btrfs filesystem overview highlights some longstanding shortcomings.
September 24, 2021
https://arstechnica.com/gadgets/2021/09/examining-btrfs-linuxs-perpetually-half-finished-filesystem/

Btrfs—short for "B-Tree File System" and frequently pronounced "butter" or "butter eff ess"—is the most advanced filesystem present in the mainline Linux kernel. In some ways, btrfs simply seeks to supplant ext4, the default filesystem for most Linux distributions. But btrfs also aims to provide next-gen features that break the simple "filesystem" mold, combining the functionality of a RAID array manager, a volume manager, and more.

We have good news and bad news about this. First, btrfs is a perfectly cromulent single-disk ext4 replacement. But if you're hoping to replace ZFS—or a more complex stack built on discrete RAID management, volume management, and simple filesystem—the picture isn't quite so rosy. Although the btrfs project has fixed many of the glaring problems it launched with in 2009, other problems remain essentially unchanged 12 years later.
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Conclusions
Believe it or not, we've still only scratched the surface of btrfs problems. Similar problems and papercuts lurk in the way it manages snapshots, replication, compression, and more. Once we get through that, there's performance to talk about—which in many cases can be orders of magnitude slower than either ZFS or mdraid in reasonable, common real-world conditions and configurations.

We'll return to this analysis in the near future. In the meantime, if you're going to run btrfs in any configuration in which it manages multiple disks—as opposed to, eg., Synology and Netgear NAS devices, which crucially layer btrfs on top of traditional systems like LVM to avoid these pitfalls—please do so very carefully.
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