LVM + dm-cache (unencrypted)

NOTE: This partition scheme is tailored towards a desktop computer setup with enough RAM and no SWAP (and therefore no hibernate/suspend-to-disk support).

CAUTION: This setup does NOT utilize LUKS disk encryption.

LVM cache combines the benefits of a fast mass storage device (e.g. SSD) with a slow mass storage device (HDD), utilizing the former as a read/write cache for the latter. This allows the system to manage blocks of data in a way such that often used blocks are kept on the fast cache device, making the whole system a lot more responsive. Over time the cache device fills up with frequently accessed data and the system accesses the cache device more often than the origin device (the HDD). This can be used to cost-effectively speed up an inexpensive large storage device (think Apple Fusion Drive).

This guide assumes the following:

/dev/nvme0n1 is the primary disk (cache device)
/dev/sda is the secondary disk (origin device)

Nomenclature

Expression	Abbreviation	Meaning
Physical Volume	PV	Unix block device node, usable for storage by LVM. Examples: a hard disk, an MBR or GPT partition.
Volume Group	VG	Group of PVs that serves as a container for LVs. PEs are allocated from a VG for a LV.
Logical Volume	LV	"Virtual/logical partition" that resides in a VG and is composed of PEs. LVs are Unix block devices analogous to physical partitions, e.g. they can be directly formatted with a file system.
Physical Extents	PE	The smallest contiguous extent (default 4 MiB) in the PV that can be assigned to a LV. Think of PEs as parts of PVs that can be allocated to any LV.

Preparing the cache device

List available disks
```
fdisk -l
```
Start partitionaing tool for primary disk (cfdisk is a little easier to use as it has a nice TUI)

WARNING: Make sure to select your actually desired device!
```
cfdisk /dev/nvme0n1
```
Partition with the following scheme

FS Type Size Mount Point Comment

| vfat | 1G | /boot | EFI System | | LVM | (remaining) | | Linux LVM |

Preparing the origin device

Start partioning tool for secondary disk

WARNING: Make sure to select your actually desired device!
```
cfdisk /dev/sda
```
Partition with the following scheme

FS Type Size Mount Point Comment

| LVM | (all) | | Linux LVM |

Creating physical volumes, volume group and logical volumes

Create LVM physical volumes

pvcreate /dev/nvme0n1p2   # SSD
pvcreate /dev/sda1        # HDD

Create LVM volume group

NOTE: vg0 is used as an example here. Use whatever you like.
```
vgcreate vg0 /dev/nvme0n1p2 /dev/sda1
```

Create LVM logical volumes

lvcreate -l 100%FREE -n lv_root vg0 /dev/sda1
lvcreate --type cache-pool -n lv_cache -l 100%FREE vg0 /dev/nvme0n1p2

# Link cache devices
lvconvert --type cache --cachepool vg0/lv_cache vg0/lv_root

Formatting devices

Create partitions

mkfs.fat -F 32 /dev/nvme0n1p1        # EFI System Partition
mkfs.btrfs /dev/mapper/vg0-lv_root   # Btrfs root file system

Create Btrfs subvolumes

# First, mount root file system
mount /dev/mapper/vg0-lv_root /mnt

# Create subvolumes
btrfs subvolume create /mnt/@
btrfs subvolume create /mnt/@home

Mount partitions

# Unmount the root file system
umount -R /mnt

# Mount the @ subvolume
mount /dev/mapper/vg0-lv_root -o noatime,compress-force=zstd,space_cache=v2,subvol=@ /mnt

# Create mountpoints
mkdir -p /mnt/{boot,home}

# Mount the remaining partitions/subvolumes
mount /dev/nvme0n1p1 /mnt/boot
mount /dev/mapper/vg0-lv_root -o noatime,compress-force=zstd,space_cache=v2,subvol=@home /mnt/home