What happens if a host with LVM thin-provisioning runs out of space?

asked 2020-04-17 14:07:49 -0500

qumulus gravatar image

I've set up a cluster where each compute node is installed with cinder and LVM backend, with thin provisioning. Each compute host has 4 TB disk space to host the cinder/LVM Logical volumes. With thin provisioning, the hypervisor can allow the creation/placement of empty volumes that add up to larger than 4TB. This is fine if the volumes are brand new and have not reached capacity.

Let's say that users are creating VMs and volumes and are writing data. Let's say a host has 10TB total LV size. Initially, there is no issue because thin provisioning would allow this. What if the volumes are constantly being written to and at some point one VM writes to a volume that would cause the total volume capacity within a host to be larger than 4TB? Would there be some error that would corrupt this volume and others in the host? Will the new write be ignored and no other side effects after that?

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If there is not enough space to write to a thin volume, an I/O error is generated. I can't say how Cinder handles such an error, but it should not cause any corruption in other volumes. An LVM extent that is allocated to a volume will remain allocated to that volume.

Bernd Bausch gravatar imageBernd Bausch ( 2020-04-17 20:00:52 -0500 )edit