[PC-BSD Testing] Swap and root partition sizes... wtf?

Arthur A-Koziol at neiu.edu
Wed Aug 24 18:41:19 PDT 2011


On 08/24/2011 2:41 PM, Kris Moore wrote:
> On 08/24/2011 15:37, Bruce Cran wrote:
>    
>> On 24/08/2011 20:36, Jamie Ivanov wrote:
>>      
>>> 2*mem was the rule of thumb 10 years ago. I've run bsd from 486's to
>>> multi-core xeon servers, I have *never* used more than 1G swap. Back
>>> in those 486 days the rule of thumb applied. But still, 9G of swap?
>>> Its simple to incorporate your "rule of thumb" with a logical limiter
>>> so nobody waste 9G on swap. With 4G of ram, I doubt swap will ever be
>>> used, it hasn't yet.
>>>        
>> I have a machine with 16GB RAM and would be rather disappointed if I
>> saw that 32GB of disk space was used for swap :)
>>
>>      
> What do you think the upper-limit should be on SWAP then? 2/4 or higher?
>    

Kris,

<2 Cents>
The fixed swap size for Unix *is* a vestige of the olden days and it 
doesn't afford the luxury of dynamic adjustment like Windows does (i.e., 
System Managed size). The old Microsoft rule used to be swap should be 
fixed at 1.5*(Physical) RAM but that was back in the days when systems 
had 256MB to a gig. Here in the 21st century, Microsoft is using System 
Managed swap sizes by default but the average RAM in today's machine is 
4-8GB. However, I do still see swaps following the 1.5*RAM rule more or 
less.

The reality is: 1) RAM is cheap and plentiful, 2) HD space is cheap and 
plentiful (SSDs aside). While it's nice to drop an install onto an aging 
old dinosaur with 256MB RAM and get the warm fuzzy feeling in one's 
stomach, that, I feel, is a niche market, proverbially speaking. I don't 
know about you but I see a lot of dropping of i486 support in favor of 
i686. So, target what is 2-3 years old and I think it will stand.

I don't know what or if there is a magic formula, but if it could be 
scripted to detect, say, 0-512MB RAM = 128MB swap, 512-1GB RAM = 256MB 
swap, 1GB-2GB RAM = 512MB swap, 2-4GB RAM = 1GB swap, 4-8GB RAM = 2GB 
swap, 8GB+ 4GB swap. Anything more I think is excessive. If you have 
8GB+ of RAM, you won't be swapping much I would think. That is more than 
enough RAM or suffice for even the hungriest of apps. Is there anything 
out there app-wise that would minimally require 8GB? If so, that would 
be far and outside the scope of PC-BSD, no?
</2 Cents>

Arthur


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