feat: btrfs

filesystem/btrfs.md

@@ -9,10 +9,97 @@ BTRFS 的主要特性：
 
 - [Btrfs - Arch Wiki](https://wiki.archlinuxcn.org/zh-hans/Btrfs)
 
+With Btrfs, it's also easy to install and manage multiple Linux distributions on the same disk, just use different subvolumes for each distribution.
+
+## Take a snapshot of a subvolume
+
+```bash
+# create a readonly snapshot of the subvolume
+btrfs subvolume snapshot -r /home /snapshots/@home-2021-01-01
+
+# restore the snapshot
+## 1. delete the current subvolume
+btrfs subvolume delete /home
+## 2. create a new subvolume with the same name as the deleted one, using the snapshot as the source
+btrfs subvolume snapshot /snapshots/@home-2021-01-01 /home
+
+# transfer the snapshot and restore it on another machine
+btrfs send /snapshots/@home-2021-01-01 | zstd | ssh [email protected] 'zstd -d | btrfs receive /home'
+```
+
 ## Deduplication 去重功能
 
 Btrfs 本身支持去重
 
 第三方工具：
 
 - [duperemove](https://github.com/markfasheh/duperemove)
+
+## Usage
+
+```bash
+# format the root partition with btrfs and label it
+mkfs.btrfs -L crypted-nixos /dev/mapper/crypted-nixos 
+
+# mount the root partition and create subvolumes
+mount /dev/mapper/crypted-nixos /mnt
+btrfs subvolume create /mnt/@root
+btrfs subvolume create /mnt/@home
+btrfs subvolume create /mnt/@nix
+btrfs subvolume create /mnt/@swap
+umount /mnt
+
+# Remount the root partition with the subvolumes you just created
+# 
+# Enable zstd compression to:
+#   1. Reduce the read/write operations, which helps to:
+#     1. Extend the life of the SSD.
+#     2. improve the performance of disks with low IOPS / RW throughput, such as HDD and SATA SSD.
+#   2. Save the disk space.
+mount -o compress-force=zstd:1,subvol=@root /dev/mapper/crypted-nixos /mnt
+mkdir /mnt/{home,nix,swap,boot}
+mount -o compress-force=zstd:1,subvol=@home /dev/mapper/crypted-nixos /mnt/home
+mount -o compress-force=zstd:1,noatime,subvol=@nix /dev/mapper/crypted-nixos /mnt/nix
+
+
+mount -o subvol=@swap /dev/mapper/crypted-nixos /mnt/swap
+# disable CoW / compression on the swap subvolume,
+# because the linux kernel requires that swapfile must not be compressed or have copy-on-write(CoW) enabled.
+chattr -R +C -m /mnt/swap
+# put the swapfile on the swap subvolume
+cd /mnt/swap
+truncate -s 0 swapfile
+fallocate -l 96G wapfile
+chmod 600 wapfile
+mkswap swapfile
+# check whether the swap subvolume has CoW disabled
+# the output of `lsattr` for the swap subvolume should be:
+#    ---------------C------ /swap/swapfile
+# if not, delete the swapfile, and rerun the commands above.
+
+# This is an alternative way to create the swapfile on the swap subvolume:
+btrfs filesystem mkswapfile --size 96g --uuid clear /swap/swapfile
+
+lsattr /mnt/swap
+# mount the swapfile as swap area
+swapon swapfile
+```
+
+## FAQ
+
+### How to create a subvolume on top level when another subvolume is mounted on top level?
+
+```bash
+# get the uuid of the root partition
+lsblk -af
+
+# mount the root partition with the uuid
+mount /dev/disk/by-uuid/<UUID> /mnt
+
+# create a subvolume on top level
+btrfs subvolume create /mnt/@snapshots
+```
+
+
+
+