RE: [Xen-users] How many guest hosts per physical host

[svarghese <vargh@xxxxxxxxx>]

Thanks a lots for all the valuable answers.

I guess I should keep the numbers below 16 so that I don't overrun the
existing 16GB physical RAM.

Thanks.


Nathan Eisenberg wrote:
> 
>> Hi,
>> 
>> I have a Dell machine, duel core xeon, with 16GB RAM. We are planning
>> to run
>> Xen on it. The storage can be increased as required. For every guest
>> host
>> the memory that is going to be allocated is 1 GB. These guest hosts are
>> going to run web applications (apache/tomcat) for which 1 GB Ram should
>> be
>> more than sufficient.
>> 
>> Can I create more than 16 guest hosts in my physical host? If the total
>> number of host with 1GB RAM each exceeds 16, does XEN have any feature
>> to
>> mange the memory efficiently so that  memory will be allocated to guest
>> host
>> based on the load on guest hosts at a particular point of time?
> 
> The short answer is no.  You cannot overprovision RAM in XEN.
> The slightly longer answer is that overprovisioning RAM is a bad idea. 
> RAM is cheap.
> The long answer is yes.  You can provision PV linux domUs with starting
> memory, maximum memory, etc, and they can balloon as needed.
> 
> There are real, significant issues with the way ballooning works - or at
> least, there were when I last tinkered with it.  But I personally question
> the idea of over-committing a cheap resource and then introducing some
> black magic to manage it.  
> 
> Just buy another box when you fill this one up; or better yet, do a shared
> storage solution so that when you buy another box, you can move domU's to
> it so that you can take the original box down for maintenance.  Scheduling
> 15 simultaneous outages to replace one hard drive is a PITA.
> 
> Nathan
> 
> 
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> 
> 

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