November 14, 2025Nov 14 When creating a btrfs filesystem (mkfs), the -O bgt option should be set to enable the block-group-tree. This is particularly useful on large filesystems with lots of data, as mounting a large btrfs filesystem can take minutes (!!) to mount without it, vs just a couple seconds. Even just 4TiB disks I have can take around 30 seconds to mount (SSDs not such a big deal) as the filesystem has to walk the entire extent tree to mount vs with the block group tree enabled. ie benchmarks from reddit but can confirm it's the same.Some performance benchmarks:# time mount -v /mnt/Backup mount: /dev/sde mounted on /mnt/Backup. real 0m25.962s user 0m0.006s sys 0m0.282s # time mount -v /mnt/Backup mount: /dev/sde mounted on /mnt/Backup. real 0m0.610s user 0m0.005s sys 0m0.019sThe feature is supported in all kernels since 6.1 and it is a safe feature that can be rolled back with btrfs tune to disable it if users need to. Edited November 14, 2025Nov 14 by JSE
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