On Fri, Jan 12, 2007 at 10:13:08PM +0800, Tim Post wrote:
> On Fri, 2007-01-12 at 17:01 +0530, Ligesh wrote:
> >
> > Thanks.
> >
>
> I figured I'd chirp in.
>
> You guys are trying to make an exact science out of something really
> dynamic, but I agree an application educated enough to pull this off is
> sorely needed.
If we can't do exact science when we have got the kernel tighly under our
fists--or at least under an LVM--, then what's the point of it all? :-)
>
> Lets look at a small paravirtualized domain running AMP, supporting 3 -
> 5 virtual hosts, each of those vhosts is a blog, forum, wiki, something
> database driven.
>
> 2 Of them are just wordpress blogs, MyISAM tables. 3 of them use innodb
> tables (row level locking).
>
Yeah the thing is, virtuozzo has been in the industry for 5 years now, and
they have been doing mostly live backups--though of course, it is always
recommended to shut the vps down, it isn't mandatory like in the case of xen--.
So recovering from an application crash seem to be pretty much possible,
especially if it is a propery designed software. We need to scale to have the
ability to manage 10,000 vpses without every worrying about what's going on
inside each one. And this IS the real world situation, as far as hosting is
concerned.
Anyway, again, we are missing the obvious. Linux has a software suspend
feature. The thing with software suspend is that it has to sync the disk
properly, since the system has to work under normal bootup too, and thus merely
saving the state won't be sufficient to ensure data integrity. This is exactly
what Mark has been pointing out. A sync-and-save implemented in the domU. And
it can actually ensure 100% safe backups. So implementing the software suspend
inside the domU is all that we need.
xm sync-and-save domU file
snapshot domU
backup snapshot + file
xm restore domU
Regards.
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