You're probably tired of hearing this from me, but if you distribute the storage, you can evacuate all the VMs off a host, down it, do whatever, bring it back up, and then unevacuate.
> You're probably tired of hearing this from me, but if you distribute the storage, you can evacuate all the VMs off a host, down it, do whatever, bring it back up, and then unevacuate.
Yes. The same conversation is happening right now in the living room, because security has forced three reboots in the last year, after having several years where simply by being xen and pv and using pvgrub (rather than loading a user kernel from the dom0) we haven't been vulnerable to the known privilege escalations. This is a lot more labor (and customer pain) when you can't move people.
No progress on that front yet, though.
And if uptime is that important, you can just buy a server that supports PCIe hotswap.
No argument on m.2 - it's a consumer grade technology. No doubt, someone in the "cloud" space will try it... I mean, if you rely on "ephemeral disk" - well, this is just "ephemeral disk" that goes funny sooner than spinning disk.
But the problem remains, If your servers aren't disposable, if your servers can't just go away at a moment's notice, the form factor of add-in cards is going to be a problem for you, unless the add-in cards are massively more reliable than I think they are. Taking down a whole server to replace a failed disk is a no-go on most non-cloud applications...