bcache and LVM storage: Can't delete VM disk


Nov 14, 2017
If you are trying out bcache in your VM's and are using LVM storage in Proxmox, you might want to blacklist the bcache module on your host.

I use LVM over iSCSI storage for my virtual machines. I was playing around with bcache in a VM. Worked great, until I destroyed the VM: I couldn't delete the VM disks from LVM. The Proxmox kernel has bcache enabled by default and it instantly grabbed the bcache volumes. Because the disks were in use I couldn't delete them. Eventually I gave up trying to get the bcache device stopped and the disks unmounted. I just blacklisted bcache on my host in /etc/modprobe.d/ and after a reboot I could delete the orphaned disks.

bcache is easy to setup and it did give me good results but I discovered how hard it is to remove from a system. Still a good option inside a VM: The backing device can be on shared storage and the cache device can be local. No risk of data-loss if you set it to writethrough mode. Just remember to blacklist the bcache module on Proxmox first.
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