I have heard different versions of "rules of thumb" for paging space.
  I have heard both 2X and 3X real memory, spread evenly over all the
  PVs.  When you get into very large memory sizes, or very large numbers
  of disks, does this still apply?  I specifically am looking for a
  recommendation for how much paging space I should have for a 64MB
  system with 11 PVs.  If I use the rules of thumb, I would put
  somewhere between 8 and 20MB on each disk - does that sound right?  I
  realize like most things that this is all very dependent on what my
  system is doing, but if you could just help me with what the latest
  and greatest rules of thumb for paging space are, I'd appreciate it.t
  Comments on large amounts of memory systems and/or large numbers of
  disks would help me too.

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  A:     There is no such thing as the "right" amount of paging space
         for a system.    The paging space requirements are unique for
         each system, depending on such things as which applications
         are running and/or the number of active users.

         There are several "rules of thumb" used to determine how to
         create your paging space:

         Rule 1:

            The install process will create paging space equal to
            two times memory (2X) for systems with less than 64MB
            of RAM.    For systems with 64MB of RAM or more, the
            paging space will be RAM size + 16MB.    Please note
            that while this may be applicable to some computing
            environments, it may not be enough paging space for

         Rule 2:

            Set paging space equal to two times RAM.    However,
            systems with large amounts of memory typically do
            not need such large amounts of paging space.

         Rule 3:

            The "twice RAM rule" is a good starting point for
            systems with 256MB of RAM or less.    Use the
            following equation for systems with more than
            256MB of RAM:

                    Page Space = 512 + ( RAM - 256 ) * 1.25

         Things to consider when creating or enlarging paging space:

         Consideration 1:

      Do not put more than one paging space on a physical

         Reason for Consideration 1:

            All processes that are started during the boot process
            are allocated paging space on hd6.    After the additional
            paging spaces are activated, paging space is allocated in
            a "round robin" manner in 4KB "chunks".    If you have
            paging space on multiple physical volumes and you put more
            than one paging space on a physical volume, you will no
            longer be spreading your paging activity over multiple
            physical volumes.

         Consideration 2:

            Do not spread paging space over multiple physical volumes.

         Reason for Consideration 2:

            If your paging space is spread over multiple drives, you
            will not be spreading your paging activity across all of
            your physical volumes.    Add a new paging space on a
            different physical volume.

         Consideration 3:

            Make paging space a similar size as much as possible.

         Reason for Consideration 3:

            If you have paging spaces of different sizes, when the
            smaller ones becomes from, you will not longer be
            spreading your paging activity across your physical

         Consideration 4:

            Avoid putting a paging space on the same volume as a
            heavily active logical volume, such as that used by a

         Reason for Consideration 4:

            It is not necessary to put a paging space on each physical

         How will you know if you need more paging space?

            1.   A message presented on the console which
                 says "INIT: Paging space is low".

            2.   Applications will abort with the message,
                 "Not enough memory".

            3.   Use of the AIX command 'lsps -a' shows a
                 high percent used for paging space.   This
                 percent will typically be over 50 .

            4.   Other AIX command which can be used for
                 performance tuning and analysis are:

                    iostat - Reports CPU and I/O statistics

                    vmstat - Reports statistics about processes,
                             virtual memory, disks, faults, and
                             CPU activity

                     svmon - Memory and page space used by all

                      rmss - Simulate the amount of memory
                             available for paging analysis

         Finally, do not put a paging space on a removable disk drive.
         The system will crash if the disk is removed.