I did get some good responses, but I still feel that my major concern of
the maximum amount of swap is hazy. If anybody has more info on this please
feel free to mail me.
Thanks for all of the responses.
********************************************************************************
Original request:
>
> Is there a maximum amount of swap which can be configured a Sun workstation?
>
> I am most interested in sun4m Solaris 1.1 or 2.2 servers and
> Sun4d Solaris 2.2 servers.
>
> Is there a point when adding more swap begins to degrade performance?
>
> I am looking at configurations with anywhere from 256MB to 1.5GB of memory
> in a sun4m system and up to 5 GB in a sun4d (SC1000/SC1000) system.
>
********************************************************************************
Summary:
> Is there a maximum amount of swap which can be configured a Sun workstation?
One respondent stated that a 4.1.x sun4c arc has a max
swap area of 512MB which will be accessed. More can be configured, but
will not be accessed.
Nobody was positive of a maximum amount of swap on other arch/OS.
Respondents have up to 1.5GB of swap with no problems.
I have had up to 4GB of swap and 2Gb of memory on a sun4m system running
4.1.3 with no apparent problems.
> I am most interested in sun4m Solaris 1.1 or 2.2 servers and
> Sun4d Solaris 2.2 servers.
On Solaris 1.1 systems, you must have a least as much swap as memory.
I have always used the rule of 2x memory as a minimum.
We have had the experience that you cannot malloc() more memory than
you have swap. i.e. 64MB memory and 128MB of swap limits the malloc()
to 128MB.
On Solaris 2.x systems, swap is only allocated on disk when you
*really* run out of memory. Therefore, your not required to have as
much swap as memory unless.
In 1.1, you have to have all of your memory backed by swap.
In 2.x, your VM is swap+physmem, so you don't need to think of massive
amounts of swap - you can think of it as overflow.
> Is there a point when adding more swap begins to degrade performance?
the majority agree that you will not see performance go down due
to excessive amounts swap. For optimal performance spread swap equally
across multiple controllers or a least multiple disks.
There were questions about fault tolerance when multiple spindles
were used for swap and one of the spindles dies. Does the system panic?
********************************************************************************
Thanks to:
stern@sunne.east.sun.com (Hal Stern - NE Area Systems Engineer)
green@.Kodak.COM Russell J. Green
ems@ccrl.nj.nec.com Ed Strong
charlesb@nimrod.ta.oz.au (Charles Butcher)
sun@cs.st-andrews.ac.uk Colin Allison
kevin@uniq.com.au (Kevin Sheehan {Consulting Poster Child})
********************************************************************************
Full responses:
--------------------------------------------------------------------------------
>From stern@sunne.east.sun.com Wed Jul 7 22:03:29 1993
Subject: Re: Max swap ?
Status: OR
in solaris 2.x, swap is only allocated on disk when you really
run out of memory (you still are assured of having some place
to put the page, unlike IBM's current malloc()). so you don't
need say 1.5Gbyte of swap for a 1.5Gbyte system.
adding swap won't degrade performance, provided you spread its use
over several disks.
--hal
--------------------------------------------------------------------------------
>From green@kodak.com Thu Jul 8 08:38:11 1993
Subject: Re: Max swap ?
Status: OR
Keith,
I do not know of any hard limit. The type and speed of your swap device and it's
location on the bus ARE limiting factors.
Obviously, you don't want swap on you slowest device. You want the disk located on
the LEAST active bus you have for such large memory configuations.
I current have a 630MP with 320Mb of memory and 1Gb of swap. The swap disk is the
first disk in the first SCSI chain. I have no complaints.
Hope this helps,
Russ
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~ Russell J. Green | Rochester Distributed Computer Services ~
~ Mail Stop 01826 | ~
~ Eastman Kodak Company | --------------------------------------- ~
~ Rochester, NY 14650-1826 | Internet mail: green@.Kodak.COM ~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--------------------------------------------------------------------------------
>From ems@ccrl.nj.nec.com Thu Jul 8 08:26:15 1993
Subject: Re: Max swap ?
Status: OR
I know max swap in 4.1.X sun4c architecture is 512 MB. Adding more doesn't
hurt, but it cannot be accessed. I have not tried maximum swap on sun4m
or sun4d systems. I recall hearing of problems with 1.1 sun4m systems and
more that .5 GB of physical memory, although they were rated for more.
Ed Strong
--------------------------------------------------------------------------------
>From root@nimrod.ta.oz.au Wed Jul 7 23:36:51 1993
Subject: Re: Max swap ?
Keith,
I have a 690 with 512Mb of RAM and 12 x 2.1Gb disks running 4.1.3.
After talking it around with various people including a Sun techo we
opted for having a swap partition of about 150Mb on each of the disks;
this naturally maximises potential paging bandwidth. Putting all of
them on-line would then give me in excess of 1.5Gb (I've heard
suggestions of up to 5x physical memory for swap, but it depends on the
usage patterns of course). I am not using all of them right now
because the load on the machine hasn't ramped up yet.
Nobody suggested there was a point where too much swap was going to
reduce performance (but I never asked :-). I have an unresolved
question about fault tolerance when possibly every disk has a swap
partition on it and whether this in effect means that any disk failing
will panic the system. Since this will be a database server, any disk
loss will render it more or less useless anyway so we decided not to
concern ourselves with that issue too much.
When you have many swap spindles you can tune the kernel paging
parameters which normally limit the rate of paging so as not to
overload a solitary swap disk. With more (and faster, newer) spindles
you can increase this. If you are interested I can send you a
(postscript) copy of a Sun performance tuning document which covers
these (and other) issues.
Good hunting!
-- Charles Butcher | Badges! We don' need no steenking BADGES! charlesb@nimrod.ta.oz.au |-------------------------------------------------------------------------------- >From sun@cs.st-andrews.ac.uk Thu Jul 8 12:38:55 1993 Subject: Re: Max swap ?
We have 600M on Sparc LX running Solaris 2.1. It all gets used - no visible problems. Please summarise your findings.
regards, Colin Allison Univ. of St. Andrews Scotland -------------------------------------------------------------------------------- >From ups!uniq.com.au!kevin@warrane.connect.com.au Thu Jul 8 18:42:21 1993 Subject: Re: Max swap ?
[ Regarding "Max swap ?", keith@lgc.com writes on Jul 7: ]
> > Is there a maximum amount of swap which can be configured a Sun workstation? > > I am most interested in sun4m Solaris 1.1 or 2.2 servers and > Sun4d Solaris 2.2 servers.
In 1.1, you have to have all of your memory backed by swap. In 2.x, your VM is swap+physmem, so you don't need to think of massive amounts of swap - you can think of it as overflow. > > Is there a point when adding more swap begins to degrade performance?
Not really - unless you count lots of unused disk as degradation... > > I am looking at configurations with anywhere from 256MB to 1.5GB of memory > in a sun4m system and up to 5 GB in a sun4d (SC1000/SC1000) system.
Lucky you!! Kind of depends on whether you are going to be exceeding that amount of memoryy with your applications.
l & h, kev
keith
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