Making Use Of Btrfs 3-Copy/4-Copy Support For RAID1 With Linux 5.5+

Written by Michael Larabel in Linux Storage on 11 February 2020 at 12:09 AM EST. 17 Comments
With the recently released Linux 5.5 and its new features, one of the prominent changes on the storage front was the Btrfs file-system picking up new "RAID1C3" and "RAID1C4" modes for allowing either three or four copies of RAID1 data across more drives to potentially allow up to three of four drives to fail in a RAID1 array while still being able to recover that data for this file-system with its native RAID capabilities.

Now that Linux 5.5 is reaching the likes of Arch Linux, Manjaro Linux, openSUSE Tumbleweed, and others, Btrfs developer David Sterba of SUSE has written more about the more robust RAID1 handling with Linux 5.5+.

A new blog post by Sterba covers the new RAID1C3/RAID1C4 modes followed by how to actually make use of it with the new RAID1 profiles when running mkfs.btrfs. With the Btrfs balance command, it's also possible to convert an existing Btrfs file-system to use one of these 3/4-copy modes. Though in moving to either C3 or C4 modes, you lose the ability to mount the file-system on pre-5.5 kernels.

Besides offering greater redundancy against data loss, the extra copies do open up for more parallelization potential from the increased number of copies. Btrfs developers are working on a better load balancing policy and hope to have the changes potentially ready for Linux 5.7.

More details on this Linux 5.5 Btrfs RAID1C3 / RAID1C4 functionality via Sterba's blog. Support for these new profiles has also already been wired into the likes of the GRUB bootloader's Btrfs support.
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