On Fri, Sep 29, 2006 at 08:52:58AM -0700, Chris wrote:

> As a standard practice, I've always configured swap file to be double  
> the size of real ram split across system and data disk. For example,  
> 8gb on da0 and 8gb on da1 if the system has 8g real ram. In practice,  
> In 7 or 8 years, I've never seen swap used for anything but a few k  
> of inactive processes and I would imagine if real active process  
> swapping occurred, it would be an immediate indicator that the system  
> that isn't responsive enough for use anymore and requires upgrade or  
> tuning. Can't run a website process off disk and keep anyone coming  
> to the site ;-). (BTW, I'm talking only about high end servers, not  
> test boxes where I've seen lots of swapping).
> 
> I'm at the point of attempting my first gvinum software raid-5 and  
> realized, I need the entire disk storage of all three non-system  
> drives to avoid pulling an 8gb chunk out of the drive sizes. The  
> configuration is one scsi 72g system disk and 3 that will be used for  
> the raid volume. I should mention I turn off dumps, haven't found the  
> use for that in a production server since it should not be rebooting  
> or it's back in the shop and another box is taking it's place.
> 
> Is there any shortfall in performance or reliability to running  
> production with swap equal in size to the 8gb of system memory? I  
> can't think of any but don't want to make a hard to correct mistake  
> once this thing goes in. 

It really depends on the number and size of processes you will be
running.  It you have a large memory and generally run a mix of
processes that will totally fit in memory, then it probably doesn't
doesn't matter much.   But, if you run enough to actually cause 
paging - which goes to swap space - then it becomes an issue.  Also,

I think some things that get pulled to execute often can get left
in swap space and accessed more quickly that all the way from main
disk each time.  eg the system keeps track of what it has in swap and 
it is more efficient to read from swap - less overhead.   But someone 
else should know more about that than I.

////jerry

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