Re: [Xen-API] One resource pool and local lvm SR mirrored using DRBD

[George Shuklin <george.shuklin@xxxxxxxxx>]

> > FT/HA relationship more complificated then 'better/worse', they solves
> > different problems and asking for different price for this (f.e.
> > completely FT machine will run slower that normal one).
> I have to look into the definition of these. Maybe I what I refer to FT
> is just redundancy - so in that sense FT is already the thing I want to
> achieve right now.
Ok, terms:

redundancy: your host  consist of few parts: if one part is failed, 
other will continue to provide necessary data. Refer to: disks, network 
links, power units, even memory and processors.
high availability: if one of your hosts down, other will be reconfigured 
automatically to continue/restart work of failed host.
fault tolerance: your host tasks running simultaneously on two ore more 
hosts and failed host does not cause any (significant) delay in task 
execution.
Most web application works fine with HA, FT usually needed for some 
poorly written applications (like terminal servers).
> > Please note that XCP does not contain code for native XenServer HA - it
> > depends on Windows (as far as I understand), the 'HA' in XCP limited to
> > domain restart in case of crash/host reboot.
> Okay. See above I just want the thing to be fault tolerant, I can live
> with having to restart a VM in case of a host crash right now.
> I only want to make sure I can start the system on the still running
> server (given that I only utilize 50 % of both systems).
>
> Cheers,
This is not FT, this is HA. If you don't need automatic restart (e.g. 
monitoring of health), XCP will works fine.
When one of the hosts is down, you simply saying:

xe vm-reset-power-state
xe vm-start

and VM staring on any other available host in the pool.

Note: XCP have no any technology to make storage HA/FT - you need to 
find/use separate solution.
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