CentOS - Jul 2013 - How often is kernel "touching" swap partition?

Hello,

I am going to buy new laptop with two drives, one SSD and one HDD and I
want to place swap partition on HDD which will be most time unused and
therefore spinned down. Problem is, that I don't know, if or how often is
kernel touching swap space even if there is lot of free memory and thus
spinning HDD up.

Thank you in advance

Martin ??astn? wrote:
> Hello,
>
> I am going to buy new laptop with two drives, one SSD and one HDD and I
> want to place swap partition on HDD which will be most time unused and
> therefore spinned down. Problem is, that I don't know, if or how often
is
> kernel touching swap space even if there is lot of free memory and thus
> spinning HDD up.
>
You should partition your drives anyway: a small, like 1G, partition for
/boot. For swap, the old Received Wisdom was 2-2.5 times RAM; these days,
it's "make swap to be 2G (for emergencies). Put swap on the SSD, I
*guess*... if it's enterprise grade, and not "consumer grade",
which will
eventually give up with too many writes.

    mark

On 07/23/2013 01:22 PM, Martin ??astn? wrote:
>  how often is kernel touching swap space 
There's a kernel tunable called "swappiness" [1] to control that. 
You
can add an entry in /etc/sysctl.conf like this:

vm.swappiness=0

...and the kernel will avoid, as much as it can, to use swap.

HTH,
Jorge

[1]: http://en.wikipedia.org/wiki/Swappiness