How much swap space for a 32 GB RAM system?

[Michael Powell]

Littlefield, Tyler wrote:

> On 7/22/2014 12:05 PM, Arthur Chance wrote:
>> I'm getting a new machine with 32 GB of memory. The old "twice
>> physical memory" sizing seems ridiculous, so how big should I make
>> swap? Do I even need swap with this much memory?
>>
> That number was always weird and never made much sense. What swap
> ultimately comes down to though is you, the user. If you foresee needing
> more than 32 gb ram, feel free to add more swap space. If you don't,
> maybe 8 gb or so just to be on the safe side. If you really need 32 gb
> swap space, I'd recommend just getting more ram, as that will be much,
> much faster than thrashing.
> HTH,

The other consideration is crash dump. I run my servers without symbols, 
NO_PROFILE, and no kernel debugging stuff. Of course, should you actually run 
into a situation where you need to assist the devs troubleshooting you won't 
be able to do much. I use RELEASE branch(s), and only apply security updates 
so have an expected stability which I have seen in practice. From my 
viewpoint, if it works 100% when you initially setup a piece of hardware it 
will continue to work fine throughout the life cycle.

Since I don't use such things (me sysadmin - not a coder) I'm not as 
knowledgeable, but I seem to recall that a crash dump needs a swap that is 
as large as physical memory. I think there is also a mini crash dump which 
does not. I would investigate the mini crash dump requirements to see if you 
can correlate some magic number from that - e.g., a box with 32G ram needs 
an 8G swap in order to do a mini crash dump kind of thing.

At any rate having _some_ swap available is a Good Thing for a "just in 
case" scenario. It will buy you time to investigate and mitigate a runaway 
process. Other list members know more about this topic than I do, just 
wanted to point out the crash dump scenario.

-Mike