Re: W2K RAMlimits

[Robert L Krawitz <rlk@alum.mit.edu>]

   Date: Sun, 16 Jun 2002 06:28:24 -0400
   From: Bertho Boman <boman@vinland.com>

   I have not been checking on availability and sizes but it sounds
   very promising to use a larger one as a swap disk.  I also expect
   their sizes to grow as RAM prices gets lower.  I do not know why
   they are so poorly advertised in the common channels.

Using a *physical* RAM drive like that as a swap device is actually
not usually a very good idea.  The reason (as I mentioned in a
previous post) is that this RAM is not directly on the system bus, but
rather is attached to the PCI bus, which is much slower.  For OS
paging, there's no reason whatsoever to do this except to work around
limits in the amount of physical memory the OS will recognize.

If you really want to use a memory-based filesystem for
application-level swapping performance, the right thing to do is to
use some kind of RAM or virtual-memory based filesystem (in the latter
case, use the smallest swap space you can, or even don't use any swap
space if your OS allows it).  This requires an appropriate driver for
your OS, but it will be much superior to a RAM-based device that
emulates a physical disk drive.

The right use for a RAM-based disk drive like those products under
discussion is for something *non*-volatile.  In other words, this
device needs battery backup.  In this case you will get a low-latency
(but still much higher latency than normal RAM), fast disk drive
useful for holding frequently accessed data.

-- 
Robert Krawitz <rlk@alum.mit.edu>      http://www.tiac.net/users/rlk/

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