A few days ago I successfully install
bcache to my system Ubuntu 14.04. It was easy, but there is a lot confusing information on the Internet, that's why I decided to write this tutorial.
Is it safe for my data?
Yes it is safe. During installation all data will be copied to new partition.
Why do I need bcache?
My Ubuntu installed on SSD. Eventualy my root (
/) partition became larger than SSD (Low disk space on "filesystem root"). I want my computer work as fast as it can, that's why I need
bcache supports multiple
backing devices and one
caching, that mean one SSD could work as
cache for multiple partitions. For me it is
My configuration before installation
My laptop ASUS ZENBOOK UX32VD. My system configuration before installation:
- /dev/sdb - SSD
- /dev/sdb1/ -
- /dev/sdb2/ -
- /dev/sdb1/ -
- /dev/sda - HDD
- /dev/sda1 -
- /dev/sda2 -
1Gthis is for backup my
- /dev/sda3 -
30Gthis is for backup my
- /dev/sda1 -
What to do ?
- Because I already have
/dev/sda3for backing up I don't need to create new partitions. But if you don't have them, create new partition on HDD for you new root partition.
- Download Ubuntu 14.10 image, and create USB bootable Ubuntu. Important note: this Ubuntu image must have the same bit as your Ubuntu (64bit for 64bit and 32bit for 32bit). This is because we are going to run chroot.
Boot from USB, choose Try Ubuntu without installing.
install bcache tools, it should be in 14.10 repositories by default
sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu $(lsb_release -sc) universe" sudo apt-get update sudo apt-get install bcache-tools
Make new root partition (in my case /dev/sda3) backing device
wipefs -a /dev/sda3 make-bcache -B /dev/sda3 mkfs.ext4 /dev/bcache0
Mount your old
/media/root_old, and your
new root partitionas
/media/root_new. Copy all data from old to new (rsync copy):
mkdir /media/root_old mkdir /media/root_new mount /dev/sdb2 /media/root_old mount /dev/bcache /media/root_new rsync -avxHAXW --progress --numeric-ids /media/root_old /media/root_new
get UUID of
ls -l /dev/disk/by-uuid/ | grep bcache0
chroot to new root (/media/root_new) to edit fstab and to update grub:
# I have to mount `/boot` because it is on separate partition. mount /dev/sdb1 /media/root_new/boot # prepare chroot for i in /sys /dev /run /proc; do mount --bind "$i" "/media/root_new$i";done chroot /media/root_new
substitute UUID for
/etc/fstab/to UUID that you obtained on step 5
#vim /etc/fstab or #nano /etc/fstab
now update grub
exit chroot and unmount everything we mount to /media/root_new
exit umount --recursive /media/root_new
Now reboot to new created partition.
On this step you should be able to boot from new root partition, you will see it in grub menu. If you succesfully boot from new partition, proceed to next step. If not may be repeat step 6, and check UUID you obtained on step 5.
Create caching device from old root. This will erase everything from your old root partition
wipefs -a /dev/sdb2 make-bcache -C /dev/sdb2
find your caching device UUID:
now use this UUID to attach caching device to backing device
echo <UUID> > /sys/block/bcache0/bcache/attach
Check if caching is started and working:
$ tail /sys/block/bcache0/bcache/stats_total/* ==> /sys/block/bcache0/bcache/stats_total/bypassed <== 8.1G ==> /sys/block/bcache0/bcache/stats_total/cache_bypass_hits <== 352707 ==> /sys/block/bcache0/bcache/stats_total/cache_bypass_misses <== 0 ==> /sys/block/bcache0/bcache/stats_total/cache_hit_ratio <== 61 ==> /sys/block/bcache0/bcache/stats_total/cache_hits <== 187802 ==> /sys/block/bcache0/bcache/stats_total/cache_miss_collisions <== 407 ==> /sys/block/bcache0/bcache/stats_total/cache_misses <== 116714 ==> /sys/block/bcache0/bcache/stats_total/cache_readaheads <== 0
I made a simple
bcache test. I was trying to copy
.iso image of Ubuntu using dd command:
# sync && dd if=/home/c0rp/image.iso of=/image.iso bs=512k oflag=direct
I did this test a few times with
bcache turned off and turned on. Here is average copying speed.
- bcache turned on: 250-300 MB/s
- bcache turned off: 70-110 MB/s
I was turning on/off bcache by using this commands:
$ sudo su - -c 'echo none > /sys/block/bcache0/bcache/cache_mode' $ sudo su - -c 'echo writeback > /sys/block/bcache0/bcache/cache_mode'