[Gllug] Swap Restrictions

[Alan Pope]

On Tue, 2006-04-18 at 15:16 +0100, Christian Smith wrote:
> On Wed, 12 Apr 2006, Steve Nelson wrote:
> 
> >Hello All,
> >
> >
> >Finally, I have just built another two machines, both with 8G of RAM.
> >The client requested 16G of swap(!).  There weren't enough partitions
> >to make 8 x 2G partitions, and surely this is overkill anyway, even
> >for a very very busy Oracle server?  I created 3 x 2G.  Just wondered
> >what we think about such large swap partitions, and how they should be
> >created?  More extended partitions and multiples of 2G?
> 
> 
> Ask why they want 16G of swap. If it's the old 2x RAM rule, then they are
> about two decades out of date.
> 

Some application products specify a large amount of swap due to the way
they use (considerably) large amounts of memory. Take SAP BW for
example. *Minimum* swap recommended is 20GiB on a 64-bit platform.
There's loads of tech docs about it on SAPs (unfortunately non-public)
website. The basic crux being "for an enterprise app you *never* want it
to run out of memory, and as memory/disk space for swap is *relatively*
cheap (compared to consultant time analysing and resolving the issue)
you might as just give it a metric arseload of RAM and SWAP and forget
about it". Not my words, not a quote, but paraphrased from numerous SAP
OSS Notes.

For SAP R/3 (the ERP solution) the general recommendation was always
2-3xRAM as SWAP, and still is.

Cheers,
Al.


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