partitioning HD for use of swap & for booting

Robert G. Brown rgb at phy.duke.edu
Fri Jun 1 15:08:32 EDT 2001


On Fri, 1 Jun 2001, Nordwall, Douglas J wrote:

> I guess the question I have got to ask is if it is still practical to run with
> 2xmemory when you start reaching up into large memory? I assume this is only if
> you ever hit swap...

As Greg and I both said, the system will use swap if it exists for
various optimizations whether or not an application actually swaps,
although it sounds like 2.4.x might be a bit weak still on the
optimizations.  So far I haven't hit a lot of the instabilities
personally, but neither have I hammered on any of my 2.4.x based
systems.  Soon.

As for practicality, the LARGEST physical memory you are likely to have
is 1.5-2 GB per node, although there may be some deep-pocketed or custom
engineered exceptions -- one restriction is that a lot of the P3, P4 and
Athlon motherboards and chipsets come with only 2-4 slots and 512 MB
DIMMS are the biggest that are commonly available (at least) to fill
them.  The SMALLEST local disk you are likely to have on a new system is
10-20 GB; 20 GB disks are just dropping to the roughly $100 price point
which seems to be the practical minimum amount vendors are willing to
sell hard disks for.  This means that you can easily do up to 4 GB for
swap and still have at LEAST 6 GB for the OS and application scratch
space, if not 16 GB.  Hard disk has historically gotten bigger and
cheaper faster than DRAM of any sort, often doubling more than once at
constant cost in a single year.  This situation will therefore likely
persist indefinitely even in the teeth of Moore's Law for at least a few
more years.

So yes, it is practical.  If you have a (10 GB or bigger) node hard disk
at all you would be slightly crazy not to make a nice big swap.  If you
don't, you should try to get a lot of memory since we ALL agree that if
any of your applications actually swap to disk (for more than a tiny bit
of time in a given computation, at any rate), you lose big time.  I like
having a nice big VM on a node or workstation configuration to avoid
instant systems death on a memory leak or load peak or when running a
memory pig (there are a number of memory-hog workstation apps:
mathematica, netscape, acroread, some of the hi-res graphics tools), but
I try never to actually use it as "swap".

   rgb

-- 
Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu




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