We have some CentOS 7 qemu/kvm servers for hosting dev/test VMs, where the backing VM images are stored to a local RAID array formatted with XFS. Basically a 2

We have some CentOS 7 qemu/kvm servers for hosting dev/test VMs, where the backing VM images are stored to a local RAID array formatted with XFS. Basically a 2-socket server with 128-256GB RAM and an LSI MegaRAID controller with battery-backed, write-back caching. Each virtual disk in a VM is a raw-formatted file in the host filesystem. We have seen host kernel panics which damage the filesystem such that xfs_repair cannot fix it. It could be mounted read-only, though I am not sure I would trust the content. We just reformatted and rebuilt content from external sources. What I believe caused this panic was a habit of creating sparse VM disk images. Later, under heavy write loads from multiple VMs, the host OS filesystem seemed to choke under all the out-of-order allocation needed to place new data into those sparse disk images. When we instituted a policy of always preallocating the VM disk files, we never saw this problem repeated.