Create lvm-cache.md

docs/setup/storage/lvm-cache.md

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+---
+title: LVM Cache
+description: How to create LVM setup with LVM Cache
+weight: 10
+aliases:
+    - ../../os/lvm-cache
+---
+
+
+From lvmcache(7):
+
+> The cache logical volume type uses a small and fast LV to improve the performance of a large and slow LV. It does this by storing the frequently used blocks on the faster LV. LVM refers to the small fast LV as a cache pool LV. The large slow LV is called the origin LV. D
+
+
+**Setting up the LVM cache**
+
+You can create the LVM setup with [pvcreate](https://linux.die.net/man/8/pvcreate), [vgcreate](https://linux.die.net/man/8/vgcreate), [lvcreate](https://linux.die.net/man/8/lvcreate), and [lvconvert]([https://linux.die.net/man/8/pvcreate](https://linux.die.net/man/8/lvconvert)) traditionally. See below:
+
+For Flatcar you could use a butane configuration file for the same that would be transpiled to ignition for the same purpose (upload a script for your setup based on above somewhere): 
+
+The following is a Butane YAML config - replace the `...` placeholders with your desired values:
+
+```
+variant: flatcar
+version: 1.0.0
+systemd:
+  units:
+    - name: lvm-cache-setup.service
+      enabled: true
+      contents: |
+        [Unit]
+        Description=LVM Cachesetup
+        ConditionFirstBoot=yes
+        Before=local-fs-pre.target
+        [Service]
+        Type=oneshot
+        Restart=on-failure
+        RemainAfterExit=yes
+        ExecStart=.../lvm-cache.sh
+        [Install]
+        WantedBy=multi-user.target
+    - name: llvm-cache.mount
+      enabled: true
+      contents: |
+        [Unit]
+        Description=LVM Mount
+        [Mount]
+        What=/dev/cache-layer-vg/data
+        Where="${DIRECTORYTOMOUNTVOLUME}"
+        Type=ext4
+        Options=defaults
+        [Install]
+        WantedBy=local-fs.target
+storage:
+  files:
+    - path: .../lvm-cache.sh
+      mode: 0744
+      contents:
+        inline: |
+        #!/bin/bash
+        set -euo pipefail
+
+        # Define variables
+        VOLUME="/dev/...."
+        DEVA="/dev/..."
+        DEVB="/dev/..."
+        CACHEDISKSIZE="...G"
+        METADISKSIZE="...G"
+        DIRECTORYTOMOUNTVOLUME="...."
+
+        # Create Physical Volumes
+        pvcreate "${VOLUME}" "${DEVA}" "${DEVB}"
+
+        # Create Volume Group
+        vgcreate cache-layer-vg "$VOLUME" "$DEVA" "$DEVB"
+
+        # Create Logical Volume for data
+        lvcreate -l 100%FREE -n data cache-layer-vg "$VOLUME"
+
+        # Create Logical Volumes for cachedisk and metadisk
+        lvcreate -L $"{CACHEDISKSIZE}" -n cachedisk cache-layer-vg
+        lvcreate -L $"{METADISKSIZE}" -n metadisk cache-layer-vg
+
+        # Convert cachedisk to cache pool with metadisk as pool metadata
+        lvconvert --type=cache-pool /dev/cache-layer-vg/cachedisk --poolmetadata /dev/cache-layer-vg/metadisk
+
+        # Convert data volume to cache volume using cachedisk as the cache pool
+        lvconvert --type cache /dev/cache-layer-vg/data --cachepool /dev/cache-layer-vg/cachedisk
+
+        # Format the data volume with ext4 filesystem
+        mkfs.ext4 /dev/cache-layer-vg/data
+
+        # Create directory for mounting the data volume
+        mkdir "${DIRECTORYTOMOUNTVOLUME}"
+
+```
+
+Then you transpile it to ignition:
+
+```
+cat cl.yaml | docker run --rm -i quay.io/coreos/butane:latest > ignition-config.json
+```
+
+