Logical Volume Manager 2 (lvm2) is a very powerful toolset to manage physical storage devices and logical volumes. I’ve been using that instead of disk partitions for over a decade now. LVM gives you full control where logical volumes are placed, and a ton of other features I have not even tried out yet. It can provide software RAID, it can provide error correction, you can move around logical volumes while they are being actively used. In short, LVM is an awesome tool that should be in every Linux-admin’s toolbox.
Today I want to show how I used LVM’s cache volume feature to drastically speed up a Btrfs RAID1 situated on two slow desktop HDDs, using two cheap SSDs also attached to the same computer, while still maintaining reasonable error resilience against single failing devices.
Creating the cached LVs and Btrfs RAID1
The setup is as follows:
- 2x 4TB HDD (slow), /dev/sda1, /dev/sdb1
- 2x 128GB SSD (consumer-grade, SATA), /dev/sdc1, /dev/sdd1
- All of these devices are part of the Volume Group
vg0 - Goal is to use Btrfs RAID1 mode instead of a MD RAID or lvmraid, because Btrfs has built-in checksums and can detect and correct problems a little bit better because it can determine which leg of the mirror is the correct one.