btrfs

• metadata
• data

btrfs filesystem show /

Label: 'fedora'  uuid: 3c6b0688-169e-4fce-8bfe-dc95771930bb
	Total devices 2 FS bytes used 92.18GiB
	devid    1 size 116.86GiB used 49.03GiB path /dev/nvme0n1p6
	devid    2 size 118.41GiB used 51.03GiB path /dev/nvme0n1p2

btrfs filesystem  df /

Data, single: total=94.00GiB, used=90.61GiB
System, RAID1: total=32.00MiB, used=16.00KiB
Metadata, RAID1: total=3.00GiB, used=1.57GiB
GlobalReserve, single: total=199.94MiB, used=0.00B

GlobalReserve - 純緊急救援, 不能手動操作

很厲害的 online 調整

btrfs balance start -dconvert=single -mconvert=raid1 /mnt

RAID-like function

• btrfs RAID 5/6 write hole
  • Write-Ahead Logging (WAL) and CoW

btrfs balance炸空間

• zfs reservation like
  要留 unallocated 的空間 也許 10~15% (其實這個跟 zfs 的 reservation 就幾乎沒兩樣了) 等 不小心 快炸的時候 再放出來
• ka-iu 用usb 暫時增加空間 緊急救援

避免 raid 5/6

btrfs balance

Reflink

cp --reflink=always source target

cp --reflink=always /var/lib/containers/rocky8.qcow2 /var/lib/containers/rocky8-kernel-ready.qcow2

NOCOW

chattr +C

lsattr

subvolume

btrfs subvolume show /home/p123
home/p123
	Name: 			p123
	UUID: 			8c27b7eb-811f-6f43-8957-cb5a36fddf4a
	Parent UUID: 		-
	Received UUID: 		-
	Creation time: 		2024-11-26 13:15:41 +0800
	Subvolume ID: 		261
	Generation: 		348697
	Gen at creation: 	343745
	Parent ID: 		257
	Top level ID: 		257
	Flags: 			-
	Send transid: 		0
	Send time: 		2024-11-26 13:15:41 +0800
	Receive transid: 	0
	Receive time: 		-
	Snapshot(s):
				home/shawn/p123.x
	Quota group:		n/a

snapshots