A few years ago I had an HP Envy 6T ultra book which shipped with
Intel Smart Response software that permitted me to use the SSD
as a cache for my hard disk.
As the HDD operated at 5400 RPM, the SSD cache resulted in a noticeable
improvement in performance in Windows.
Sadly, at the time there was not any similar functionality in Linux.
As you can imagine, I was quite ecstatic when I learned about
Shortly after bcache was added to the kernel, I tried it out and
wrote up a short blog post about
installing bcache on Ubuntu 14.04
but honestly the method was horrible.
It involved first installing Ubuntu to a small partition, booting,
bcache device, copying the installation to the
partition, updating a bunch of things within a
fixing UUID entries in
grub, and converting the small partition to
Urgh, I know. This method is horribly complicated, prone to mistake,
and very time consuming.
Today I’m writing to say that there is a better method!
Recently I picked up a Gigabyte P34w v5 ultrabook(ish) laptop for which I wanted to use bcache, but due to some kernel bugs on Skylake processors (more on this in a later blog post), I needed to upgrade my kernel and install NVIDIA drivers immediately to keep my system from locking up. The answer was to get Ubuntu to do a bcache installation to rootfs from the get-go.
Before we get going, not that this is only valid for a new installation of Linux as we delete all file system information. If this isn’t what you want to do, I suggest you check out flashcache or EnhanceIO which will let you migrate a live system.
Here are the major steps:
- Boot the Ubuntu installer
- Create a partitions for
/boot, the backing, and cache devices.
- Create the
- Install Ubuntu onto
- While still in the live CD,
chrootinto the new installation
- Reboot into a fully functional system.
No copying full partitions, no messing with UUIDs, and no grub trickery.
Properly acknowledging my sources, there are two critical posts on
StackOverflow that made me think I could get away with this scheme:
alex’s answer on how to setup bcache and
Lekensteyn’s answer on how to restore kernels
Lastly, be aware that Grub (and Grub2) do not support bcache, so you will
need a separate
First, if you have used this system for anything important, back up your data. We’ll be erasing everything shortly.
Now, boot into the Ubuntu installer and remove any unnecessary
You can use
fdisk on the command line or the
gparted GUI for this.
Now, lets assume that your SSD is
/dev/sda and your hard disk is
/dev/sdb. Create the following partitioning scheme:
/dev/sda1 - 1024 MB, EXT4, used for /boot /dev/sda2 - any format, for cache /dev/sdb1 - EFI partition (if your machine needs it) /dev/sdb2 - swap /dev/sdb3 - any format, backing partition
Don’t worry about doing a deep format of the caching and backing
partitions as we’ll wipe these shortly.
If you made any major changes to the partition tables, you might
need to reboot before you can proceed.
gparted, in particular, will let you know if this is the case.
Loading bcache, creating device
First, connect to the Internet. Make sure the connection is working. Next open up a terminal and wipe the cache and backing partition file systems:
sudo wipefs -a /dev/sda2 sudo wifefs -a /dev/sdb3
Next we will install
bcache-tools and create the
sudo apt-get update sudo apt-get install bcache-tools sudo make-bcache -B /dev/sdb3 -C /dev/sda2 sudo mkfs.ext4 /dev/bcache0
Notice the command to
make-bcache used the HDD partition,
as the backing (
-B) device and the SDD partition,
the cache (
WITHOUT rebooting, run the Ubuntu installer from the desktop. When you get to the installation type screen which lets you pick how to install the OS (e.g. the page that says “Erase disk and install Ubuntu” or “Something else”) choose to do custom partitioning.
In the partitioning dialog configure the following:
/dev/bcache0 - format EXT4, use as / /dev/sda1 - format EXT4, use as /boot /dev/sdb1 - EFI partition (if your machine needs it) /dev/sdb2 - swap
Proceed with the installation as normal.
When it completes DO NOT REBOOT as the
initramfs installed by the
live CD does not have the
bcache kernel module.
If you accidentally rebooted, simply go back in to the live image,
bcache-tools package as described above and continue
with the instructions below.
Installing bcache on the new installation
Here is where things get tricky.
What we’re going to do is switch to the new operating system without
booting and install some software to get
and a new
initramfs generated so the computer will boot.
First we are going to create a valid
We start by mounting several directories from the new installation
into specific subdirectories in order to create the directory structure
Ubuntu Linux expects:
sudo mount /dev/bcache0 /mnt sudo mount /dev/sda1 /mnt/boot sudo mount --bind /dev /mnt/dev sudo mount --bind /proc /mnt/proc sudo mount --bind /sys /mnt/sys
Because we will need Internet access, we need to copy the DNS
configuration from the live CD into the
sudo cp /etc/resolv.conf /mnt/etc/resolv.conf
Next we put ourselves into the
sudo chroot /mnt
Now we are effectively within the new installation’s file system.
So all we need to do is install
sudo apt-get update sudo apt-get install bcache-tools
After the package is installed, you should notice that the
is re-generated and installed.
You can check the timestamps on the files in
confirm this is the case.
Now we clean up. Exit the
chroot, cleanly dismount the file system,
exit sudo umount /mnt/sys sudo umount /mnt/proc sudo umount /mnt/dev sudo umount /mnt/boot sudo umount /mnt sudo reboot
Restore the default
sudo ln -sf ../run/resolvconf/resolv.conf /etc/resolv.conf
With any luck, your machine will reboot normally and you will have a
fully functional Ubuntu installation with
bcache out of the box without
all the work of previous methods.