On 30/11/16 09:13, Yaniv Kaul wrote:
> Thanks, but it really makes no sense to me. The direct IO by the VMs is
> going to a different storage than what the host is writing to, in most
> cases.
> The host would write to the local disk, the VMs - to a shared storage,
> across NFS or block layer or so. Moreover, their IO is not buffered.
> There is very little IO coming from the host itself, generally (I hope
> so!).
>
> Partially unrelated - the trend today is actually to put NOOP on the VMs -
> the deadline is quite meaningless, as the host scheduler will reschedule
> anyway as it see fits.
> Most likely it is also a deadline scheduler (but could be NOOP as well if
> it's an all flash array, for example). Therefore there is no reason for
> anything but simple NOOP on the VMs themselves.
>
> In short, I think it's an outdated decision that perhaps should be
> revisited. Not urgent, though.
> Y.

I know it's not the most cared about usecase
but I'd like to add that this might affect local storage
domains, which I happen to use a lot, and maybe others too.

--
Mit freundlichen Grüßen / Regards

Sven Kieske

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