Re: a few may be wiki question

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Farkas Levente wrote:
>>
>>>   - is dynamic use of RAM for host operating system supported?
>>>   
>>>       
>> What's that?
>>     
>
> ok i try explain our plan and ask a better question about the memory
> setup. this may clean things a bit. i like to setup a server for the
> development dept. which compiles softwares. we need to compile on
> different platforms so we need:
> - one main server for the development (svn, trac, pxe boot, web, email
> etc, plus compile and test) centos 5 normally just this guest have some
> load.
> - mandrake 8.2 and mandrake 10 (to compile and test) don't have any
> load, but during compile they have high cpu and disk load.
> - windows may be two different 2000 and XP (to compile and test) don't
> have any load, but during compile they have high cpu and disk load.
>
> so i need a host and about 4 guest (i assume it also not recommended to
> use the host for others just to run the guests?!). i assume 4GB ram and
> think about:
> - 256MB for the host. is there any reason to give more memory for the
> host if it's only running the guests (kernel, ntp, local mail, ssh
> nothing else running on it).
> - -m 2000 for centos 5
> - -m 768 for each mandrake and windows
> fist of all is it possible to give more dynamic memory for guests as the
> sum of the whole memory? if not what is the purpose of dynamic memory?
> is the host can also dynamically get/steal memory from guests? or even i
> can give -m 2000 for all guest and the host and they will try to compete
> for the memory?
>   

There are two answers to this:

- balloon driver (like in Xen) which allows the host to move memory from 
one guest to another (or from host to guest)
- swapping, which allows the host to move guest memory to disk and 
allocate it to another guest

Unfortunately the balloon driver has not been publicly released yet, and 
swapping is still in early development, so for now you will have to use 
static allocation.


> so in short in the above setup what is the recommended config for the
> host and for the guest os?
>   

It really depends on the workload.  256MB for the host is fine, though.

>   
>>>   - what is the recommended guest disk image format? should i use an lvm
>>>     partition as guest os partition (like in xen)? what is the
>>>     recommended format assuming that may be later i'd like to add new
>>>     guests and what is the performance differences (ie. which is the
>>>     fastest format)?
>>>   
>>>       
>> Depends on workload.  lvm is fastest, qcow2 is most flexible and
>> managable.  If your guest is not issuing significant disk I/O, I'd
>> recommend qcow2.  Otherwise lvm.
>>     
>
> what does the "flexible and managable" means?
> i plan the whole system is on 2 x 250gb hdd in a raid1 and the host and
> each guest has an lvm partition as /.
>
>   

Flexible means you don't need to allocate all disk space up front, it 
grows as necessary.  With lvm you can defer allocation, but you need 
manual intervention (and changes in the guest) in order to use more 
storage.  It's also easier to back up, move around, etc.

If you have enough space, then lvm can be a good choice.  Certainly it 
gives the best performance.

-- 
error compiling committee.c: too many arguments to function


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