[conspire] Re: RHL 9 Install problems

Rick Moen rick at linuxmafia.com
Sun Jul 13 08:34:19 PDT 2003

Quoting myself:

> o  And swap, of course.  At least one partition on each physical drive.
>    Ignore the guidelines about "3X physical RAM" and such, as they're 
>    drivel.  Use your sense of what amount of swap might be actually
>    needed, when your machine is stressed.  Put it where you think it
>    will not create "thrashing" problems (excessive seeking).

I should elaborate on that "drivel" comment.

The "3X physical RAM" bit (as indicating how to estimate how much swap
space you'll need) has been a bit of Unix folklore for sysadmins for
decades.  But it doesn't work.

Consider a machine that has _8 MB_ of physical RAM -- with one of today's
usual generic 40 GB hard drives.  The rule of thumb would say allocate
24 MB of swap, out of 40 GB available.  But that's stupid:  Running that
starved on operating RAM, you'll probably have very intensive need for
swap, and can actually spare gobs of it from your available hard drive
space.  So, following the guideline would needlessly cripple your
system, shorting it very badly on virtual memory.

At the other extreme, consider a machine with 1 GB of physical RAM, and
an old 6 GB hard drive.  The odds are that, while using such a machine
even quite heavily, you'll not be even coming close to loading up all of
that physical RAM.  Yet, the rule of thumb would say splurge half your
storage on swap that won't even be used at all.

A more realistic way to estimate swap requirements is to eyeball what
sort of RAM loading you expect to subject the machine to, and then
furnish the shortfall above and beyond physical RAM, plus a safety
margin in addition.  If you have hard drive space to burn, then be
generous, as it never hurts to have some to spare.

Cheers,     "In 1993, the World-Wide Web was an infosystem based on hypertext.
Rick Moen    In 1994, the World-Wide Web was an infosystem based on hype."
rick at linuxmafia.com                                       -- Lars Aronsson

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