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:
- Open terminal
- Switch to root user:
- if needed make a backup of /home on your root filesystem:
cp -a /home /home.backup
- comment /home out in your /etc/fstab
- unmount /home:
- 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:
- create a new filesystem on /dev/bcache0:
mkfs -t ext4 -L ROOTFS /dev/bcache0
- mount it:
mount /dev/bcache0 /mnt
- copy your current root filesystem to /mnt:
cp -ax / /mnt
- 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:
- rename your current initramfs:
uname -r.img /boot/initramfs-
- build a new initramfs with all drivers (including bcache) included:
Now reboot your system.
- while booting edit the default grub entry and replace the root=UUID=... parameter in the "linux" line by: root=LABEL=ROOTFS
- 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:
- update grub config:
grub2-mkconfig -o /boot/grub2/grub.cfgfor BIOS systems and
grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfgfor UEFI systems
- rename your current initramfs (again):
uname -r.img /boot/initramfs-
- build a new initramfs with only the needed drivers included:
Now your system should be ready!
- reboot your system to see if it boots OK.
- apply updates:
yum update. Specifically try to update the kernel, because it depens on the proper interaction between dracut, bcache-tools and util-linux,
- All steps complete without errors
- 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:
- note the starting start position of /dev/sda2
- remove partitions /dev/sda2, /dev/sda3 and /dev/vda4
- recreate /dev/sda2 and make sure the start position is the number you noted before
- write the new partition table to disk
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.
- resize the root filesystem:
- use df to check the filesystem's size