Hi Aryeh,
Does this bring up the same power failure scenario issues mentioned in
the link you provided?    It seems like the only way to get reasonable
performance is to be essentially unsafe in guest writes to the host

 Use ZFS and a ZIL to mitigate this. Or UFS with journalling.

 A question does the ability of FreeBSD to be able to better
handle power failure in general better then linux (it seems like every
time there is a unscheduled reboot on linux it messes up)?

 It's not the o/s but the behavior of the filesystem.

  This seems
to be at odds with my personal observations of bhyve via petitecloud
which I routinely very abruptly start/stop (petitecloud's "stop" is
nothing more then killing the hyperv and any cleanup needed) and except
for the occasional need for a fsck have not had an issue.

It's not the VM stop/crash that's the problem, but the host. Once a write has been marked as complete by the VM, the guest assumes it has been committed to stable storage and can assume e.g. that a database transaction is complete.

If the write is being held in the host's buffer cache and power is lost, the write never makes it to stable storage, resulting in data loss/corruption for the guest. This is different than the VM crashing, since the writes in the host's buffer cache aren't lost in that case.



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