some interesting observations on the relative performance of kvm vs. bhyve

[Peter Grehan]

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
> disk?

  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.

later,

Peter.