Re: [sami] Welcome to SAMI and something you may like to know.

[Melinda Shore <[e-mail]>]

On 8/18/11 4:57 AM, Yingjie Gu(yingjie) wrote:
> We need to be aware that, not all L2 subnet has enough bandwidth or shared storage or reasonable migration distance to make VM migration succeed. In our scope, I suggest we only consider the L2 subnet which can support successful VM migration, in which case we has the reason to consider state migration. Let's call it "qualified L2 subnet", which equals to Yongbing's " L2 subnet with good enough performance ". It should be the users of "State Migration mechanism" to judge whether their L2 subnet is suitable for VM Migration and whether they should adopt State Migration mechanism in their subnet.
> Of course, even in a "qualified L2 subnet", VM migration can not be successful all the time. So, we also need to consider failure feedback mechanism.

Absolutely.  It seems to me that if you think that - for the purposes
of state migration - failing because there's insufficient network
resources is different from failing for some other reason, it might be
a good thing to explain why.  I could be convinced otherwise but for
the moment I don't think this is a particularly defensible distinction.

I'm also not clear on how much network bandwidth is needed to support
failover.  Intuitively it seems like the answer is "nearly none."
There may be issues around bandwidth available to the hot spare when
it goes live but if they're on the same layer 2 subnet/network segment,
the failed-from and failed-to servers are going to have pretty much
the same resources available to them.

Melinda