ITEM: G8968

How much paging space do I need?

Question:

How much paging space do I need for my system?

Response:

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 runing and/or the number of active users.

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

1)  The install process will create paging space equal to 2 times memory for
    systems with less than 64MB of RAM.  For systems with 64MB of RAM or
    more, paging space will be RAM size + 16MB.
     While this equation may work for some systems, this is not enough paging
    space for many systems.

2)  Another "rule of thumb" is to set paging space equal to 2 times RAM. 
    The problem with this rule is that systems with large amounts of memory
    typically do not need such large paging space requirements.

3)  The last "rule of thumb"....
    For systems with 256MB of RAM or less, the 2 times RAM rule is a good
    starting point.  For systems with greater than 256MB RAM, use the
    following equation:

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

Things to consider when creating or enlarging your paging space.
1)  Do not put more than one paging space on a physical volume.  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 fashion 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.
2)  Do not spread a paging space over multiple physical volumes.  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.
3)  Try to have your paging space of similar size.  If you have paging spaces
    of different sizes, when the smaller ones become full, you will no longer
    be spreading your paging activity across your physical volumes.
4)  It is not necessary to put a paging space on each physical volume.  Avoid
    putting a paging space on the same volume as a heavily active logical
    volume (such as a database).

"How do I know if I need more paging space?"
1)  You may see "INIT: Paging space is low" messages on the console.
2)  You may have applications aborting with messages regarding "Not enough
    memory".
3)  An "lsps -a" shows high percent used for your existing paging spaces.
4)  Do not put a paging space on a removable disk drive.  The system will crash
    if the drive is removed.



Support Line: How much paging space do I need? ITEM: G8968

Dated: February 1994 Category: N/A

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