[aklug] Re: swapping (was Re: What should I consider before doing an install? )

On 07/07/2011 10:30 AM, The Don Lachlan wrote:
> On Tue, Jul 05, 2011 at 10:51:07AM -0800, Thomison, Lee wrote:
>> My first reaction is that if your machine is doing much swapping at all
>> the n you need more ram. RAM is cheap. Swap memory -really- slows things
>> down (swap thrashing), and ideally is only used for 'medium term parking',
>> rath er than active use. Even with 15K SAS, you still get a serious
>> performance hit when swap starts being used for active use.
> This is incorrect. Allocating more swap does not reduce your performance
> (it'd be pretty silly if it did).
>
I think that back in the day (kernel 2.2? Arthur would probably know)
allocating *too* much swap would hurt performance of the system. At
this time, it makes no difference how much you allocate. On most 'bare
metal' installs of servers I do, I give a decent amount of disk space to
swap, simply since it might use it, even though if a server starts
pushing into swap, I start to fiddle with things to take it back OUT of
swap. I give enough RAM so that they shouldn't require any.

> Scott,
>
> To your question about using swap space in the VM host, for what are you
> using the swap space? Each VM should have its own swap file and the host
> shouldn't allocate swap space to the VM as if it were physical memory. As
> such, I can't imagine why VirtualBox would use 5GB of swap space.
>
I can't speak for VirtualBox ( I run it on my desktop at work, but I
haven't figured out how to tell if it is allocating swap or not) but
with VMWare, occasionally the ESX/ESXi host *will* start to swap out
memory for a VM - and depending on where your swap location for the VM
in question is located, it will be from "extremely slow" (local disk) to
"so slow you want to die" (over an NFS mount.) I've found that VMWare
can be a bit hair-brained about swapping out guest memory to swap, but
that can be fixed by setting reservations under the VM's settings.

> -L
> ---------
> To unsubscribe, send email to <aklug-request@aklug.org>
> with 'unsubscribe' in the message body.
>

-- 
Adam
---------
To unsubscribe, send email to <aklug-request@aklug.org>
with 'unsubscribe' in the message body.