Swap size for large memory machines

[Bill Dana]

In article <1115 at srhqla.SR.COM>, mdh at srhqla.SR.COM (Matt Hardin) writes:
> In article <1335 at esquire>  writes:
> >What is a reasonable amount of swap space to allocate for a machine
> 
> What I am doing now is using both the b and c partitions as swap by
> issuing a swapon command for each partition (really I just defined partitions
> b and c as swap in /etc/fstab, but it works out the same way). This gives us
> ample swap space for our machine. What took me by surprise was that you could
> issue two or more swapon commands! I get to keep my standard partitions and 
> have as much swap space as I need!
> 
> The folks at Pyramid may have something to say about the performance of this
> type of configuration. I know I'd like to hear how it compares to using just
> one big swap partition...
> 
a few notes:

#1:  If you are swapping, call your pyramid sales rep and buy more memory! $-)

#2:  If swapping occures, the I/O will be interleaved accross the swap 
     partions in /etc/fstab allocated at boot time.  Thus, it is a 
     good idea to use partions on different drives.  Using (for example) 
     an 'a' and an 'e' partition on the same drive would be a good 
     exercise in seeking.  If you only have one drive, use a single 
     partition.

#3:  If /etc/swapon is used to add additional swap partitions by hand,
     interleaving will not be done on the additional drives.  
     IE:  swapping would occur on the initial partitions allocated at
     boot time (interleaved), then on the subsuqent drives configured 
     latter with /etc/swapon.

#4:  see #1.

#5:  I have been told this is how swap allocation works; I have not verified 
     it by checking out source, or by observation (I have lots of memory!)

#6: see #4.



      -m-------  Bill Dana  Performance Analyst
    ---mmm-----  Pyramid Technology Corporation		    
  -----mmmmm---  Mountain View, CA			whatever!pyramid!billd
-------mmmmmmm-  U.S.A.                                      billd at pyramid.com