libvirt users - Apr 2017 - (Live) Migration safe vs. unsafe

Hi all,

virsh checks whether a (live) migration is safe or unsafe. When a
migration is considered to be unsafe it is rejected unless the --unsafe
option is prodivided.

As a part of those checks virsh considers the cache settings for the
underlying storage resources. In this context only cache="none" is
considered to be safe.

I wonder why cache="directsync" might be harmfull as it bypasses the
host page cache completely.

Regards,

Michael

On 04/03/2017 10:07 AM, Michael Hierweck wrote:
> Hi all,
>
> virsh checks whether a (live) migration is safe or unsafe. When a
> migration is considered to be unsafe it is rejected unless the --unsafe
> option is prodivided.
>
> As a part of those checks virsh considers the cache settings for the
> underlying storage resources. In this context only cache="none"
is
> considered to be safe.
>
> I wonder why cache="directsync" might be harmfull as it bypasses
the
> host page cache completely.
That's a good question. I too think it isn't harmful. Maybe it's a
bug
in our code?

Michal