[rhelv6-beta-list] My first experiences with RHEL6 beta

[James Findley]

On 06/15/2010 02:12 PM, Jonathan S Billings wrote:
> On 06/15/2010 08:22 AM, Bryan J. Smith wrote:
>>>> When I spoke of memory being expensive compared to disk I
>>>> was speaking of how resources are limited on a system hosting
>>>> one or more virtual machines ...
>> Theoretical meta-discussions are entertaining, but ultimately help
>> few people with real systems.  Real systems really differ.  ;)
>
> I don't know what you mean about theoretical meta-discussions.
>
> Perhaps I'm being unclear.  The original post talked about avoiding
> using swap in a virtual machine.  I suggested that in a situation where
> you were running virtual machines, it costs more (in terms of limited
> resources) to add more memory to that virtual machine than it does to
> add storage.  It makes sense to add swap to a virtual machine, simply
> because the cost is low and the reward is better performance for the
> memory you do allocate.
>

In my experience, IO is such a precious and limited resource (increasing 
IO throughput, as opposed to amount of storage available, is often 
extremely expensive) that using it for swap is very counter productive. 
  I typically give VMs about 250M of swap, and set vm.swappiness to a 
very low value (sometimes even 0) in my VMs.
But I'm sure this is highly application/environment dependant, so if 
using lots of swap works for you, great.
Wanted to present a counterexample though as it isn't always the best 
thing to do.

-James