From Fedora Project Wiki


This page describes a test case for bcache-tools: "/ on bcache without using LVM"

Bcache is a Linux kernel block layer cache. It allows one or more fast disk drives such as flash-based solid state drives (SSDs) to act as a cache for one or more slower hard disk drives. The bcache-tools package contains the utilities for manipulating bcache

Testing covers not only bcache-tools but also the interaction between bcache-tools and other packages: kernel, util-linux and dracut.

Starting with a stable F20 system with /home on LVM on bcache, we can go forward and have / on bcache. Consider thought that bcache is EXPERIMENTAL!


This test requires the following test case as preparation: /home on bcache (no LVM)


If you haven't done so, you should first execute the use case /home on bcache (no LVM).

Next we'll stop using /home on bcache first:

  1. Open terminal
  2. Switch to root user: su -
  3. if needed make a backup of /home on your root filesystem: cp -a /home /home.backup
  4. comment /home out in your /etc/fstab
  5. unmount /home: umount /home
  6. if applicable restore your bachup to the /home directory: cp -a /home.backup/* /home

How to test

Now your /home is in your root filesystem. Next:

  1. create a new filesystem on /dev/bcache0: mkfs -t ext4 -L ROOTFS /dev/bcache0
  2. mount it: mount /dev/bcache0 /mnt
  3. copy your current root filesystem to /mnt: cp -ax / /mnt
  4. edit /mnt/etc/fstab so your root fs is mounted like: LABEL=ROOTFS / ext4 defaults 1 1

Now we have a duplicate root filesystem on /dev/bcache0. To use it we need to build a new initramfs:

  1. rename your current initramfs: mv /boot/initramfs-uname -r.img /boot/initramfs-uname -r.img.sav
  2. build a new initramfs with all drivers (including bcache) included: dracut -N

Now reboot your system.

  1. while booting edit the default grub entry and replace the root=UUID=... parameter in the "linux" line by: root=LABEL=ROOTFS
  2. now start the modified grub entry

If all goes well, your system now boots fine and it's running on bcache! Now we have to do some final housekeeping:

  1. update grub config: grub2-mkconfig -o /boot/grub2/grub.cfg for BIOS systems and grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg for UEFI systems
  2. rename your current initramfs (again): mv /boot/initramfs-uname -r.img /boot/initramfs-uname -r.img.sav
  3. build a new initramfs with only the needed drivers included: dracut

Now your system should be ready!

  1. reboot your system to see if it boots OK.
  2. apply updates: yum update. Specifically try to update the kernel, because it depens on the proper interaction between dracut, bcache-tools and util-linux,
  3. wget

Expected Results

  1. All steps complete without errors
  2. wget should have the same speed of all time


The only partitions used on the /dev/sda device are /dev/sda1 and /dev/sda2. We can add the rest of the disk space to the root filesystem:

  1. start fdisk /dev/sda
  2. note the starting start position of /dev/sda2
  3. remove partitions /dev/sda2, /dev/sda3 and /dev/vda4
  4. recreate /dev/sda2 and make sure the start position is the number you noted before
  5. write the new partition table to disk
  6. reboot

After the reboot the new partation table is used by the kernel. /dev/bcache0 automatically is resized because the underlying /dev/sda2 has been resized.

  1. resize the root filesystem: resiz2fs /dev/bcache0
  2. use df to check the filesystem's size