SUMMARY: Swap Space Allocations - How much is enough?

bernard.mcauley at mindspeed.com bernard.mcauley at mindspeed.com
Tue Oct 23 04:45:53 EDT 2001


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Hi,

The general response to the post below was that 4GB was far to much. 
However from there on feelings became mixed.  Most people suggest that 
2-3x physical memory was a suitable level to set the swap at.  However, 
there was a few more detailed explanations that suggest that the level can 
be lower than this.  It was highlighted by Simon Convey that having 2x 
physical memory was useful in the event of a panic, so that the entire 
physical memory could be dumped to disc for savecore to use on reboot. 
Matthew Stier points out that SunOS 4.x required 2x Physical memory for 
the kernel operation, but that with Solaris 2.x this requirement has 
disappeared and zero swap space is an option.  More importantly, he 
mentioned an Openboot bug that means that crash dump recovery only works 
with partitions up to 2GB.

Sergio Gelato highlighted the fact that /tmp is picked up from this space 
as well (important as several of the applications that we use often stream 
large files into /tmp when memory usage is at its most intense!). Finally, 
the award for a good dose of common sense goes to Ric Anderson who 
suggests running swap -r and sar -s to collect some information on Virtual 
Memory usage and make the decision based on this.  Unfortunately, this 
does require careful examination of the systems over a period of 
operation, which of course I don't have time for right now.

I have decided to go for a 2GB swap partition to avoid the problems 
highlighted by Matthew Stier and co., this will give plenty of space for 
swapping plus lots of disc space for the /tmp filesystem when it is 
strained.

Many thanks to all who contributed.

Bernard McAuley,
Mindspeed Technologies,


bernard.mcauley at mindspeed.com wrote:
> 
> Hi,
> 
> I'm updating some workstations to Solaris 2.7, and this gives me an
> opportunity to 'tune' the workstations a bit.  Currently they have 512
> MB of memory and 4GB of swap space.  I have a vauge recollection that
> 4x physical memory is a sensible level for swap space, but I have no
> idea where this figure come from.  In addition, I'm not sure how
> suitable this is for our application (CAD Workstations and IC
> Simulations).
> 
> Can anybody out there give me a feel for a sensible level of swap
> space, and more importantly, can they point me in the direction of
> some literature on the topic of swap space configuration/usage in
> solaris!
> 
> Thanks,
> 
> Bernard McAuley,
> Mindspeed Technologies,

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<br><font size=2 face="sans-serif">Hi,</font>
<br>
<br><font size=2 face="sans-serif">The general response to the post below was that 4GB was far to much. &nbsp;However from there on feelings became mixed. &nbsp;Most people suggest that 2-3x physical memory was a suitable level to set the swap at. &nbsp;However, there was a few more detailed explanations that suggest that the level can be lower than this. &nbsp;It was highlighted by Simon Convey that having 2x physical memory was useful in the event of a panic, so that the entire physical memory could be dumped to disc for savecore to use on reboot. &nbsp;Matthew Stier points out that SunOS 4.x required 2x Physical memory for the kernel operation, but that with Solaris 2.x this requirement has disappeared and zero swap space is an option. &nbsp;More importantly, he mentioned an Openboot bug that means that crash dump recovery only works with partitions up to 2GB.</font>
<br>
<br><font size=2 face="sans-serif">Sergio Gelato highlighted the fact that /tmp is picked up from this space as well (important as several of the applications that we use often stream large files into /tmp when memory usage is at its most intense!). &nbsp;Finally, the award for a good dose of common sense goes to Ric Anderson who suggests running swap -r and sar -s to collect some information on Virtual Memory usage and make the decision based on this. &nbsp;Unfortunately, this does require careful examination of the systems over a period of operation, which of course I don't have time for right now.</font>
<br>
<br><font size=2 face="sans-serif">I have decided to go for a 2GB swap partition to avoid the problems highlighted by Matthew Stier and co., this will give plenty of space for swapping plus lots of disc space for the /tmp filesystem when it is strained.</font>
<br>
<br><font size=2 face="sans-serif">Many thanks to all who contributed.</font>
<br>
<br><font size=2 face="sans-serif">Bernard McAuley,<br>
Mindspeed Technologies,<br>
</font>
<br>
<br><font size=2 face="Courier New">bernard.mcauley at mindspeed.com wrote:<br>
&gt; <br>
&gt; Hi,<br>
&gt; <br>
&gt; I'm updating some workstations to Solaris 2.7, and this gives me an<br>
&gt; opportunity to 'tune' the workstations a bit. &nbsp;Currently they have 512<br>
&gt; MB of memory and 4GB of swap space. &nbsp;I have a vauge recollection that<br>
&gt; 4x physical memory is a sensible level for swap space, but I have no<br>
&gt; idea where this figure come from. &nbsp;In addition, I'm not sure how<br>
&gt; suitable this is for our application (CAD Workstations and IC<br>
&gt; Simulations).<br>
&gt; <br>
&gt; Can anybody out there give me a feel for a sensible level of swap<br>
&gt; space, and more importantly, can they point me in the direction of<br>
&gt; some literature on the topic of swap space configuration/usage in<br>
&gt; solaris!<br>
&gt; <br>
&gt; Thanks,<br>
&gt; <br>
&gt; Bernard McAuley,<br>
&gt; Mindspeed Technologies,<br>
</font>
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