SUMMARY Swap Configuration for New V440

From: Gilliam, Kirk R. <>
Date: Thu Jan 22 2004 - 12:48:45 EST
Thanks for the replies from:
David Booth
Tim Chipman
Chris Dantos
Victor Karpovich
Wesley W. Garland
Stan Pietkiewicz
Darren Dunham

Special thanks to:

Kevin L. Prigge
Colby Johnston
Kevin Buterbaugh
Kevin L. Prigge Sent me these links for Solaris 9 and Solaris 8 respectively
and I summed it up below for Solaris 8:(Also keep in mind a large enough
space for crash dumps)

For Solaris 9:

Solaris 8:

System Type 		 				Swap Space Size
Dedicated Dump Device Size 
Workstation 4 Gbytes of physical memory 		1 Gbyte
1 Gbyte
Mid-range server 8 Gbytes of physical memory 		2 Gbytes
2 Gbytes 
High-end server 16 to 128 Gbytes of physical memory 	4 Gbytes
4 Gbytes 
Colby Johnston summed it up with following and a nice link:

I would not allocate more that 4Gb of swap unless your applications have
special swap requirements. The way sun virtualizes memory now, there is
usually no need for the old 1 to 1 ratio of physical memory to swap space.
Swap is now defined as disk backed physical memory plus a portion of real
memory. With this in mind, even though you may allocate a 4Gb swap
partition, your "swap -s" output may show you are potentially using more
than that. The "swap space" used on the system is dynamic and may not always
equal the space defined in the swap partition. 
See the following document on for a better explanation on planning the swap
space on Solaris. There is a section called "Planning for Swap space" which
should give you a good idea of how to initially configure swap.
-------------------------------------- says:
sun has changed its swap recommendations with the advent of large
amount of real memory.

under normal situations, you will never use all 16gbs of rams for
processes.  instead of swapping, your system will page (to unused
portions of real memory).  at this point, the major concern are core
dumps.  ideally you want enough swap for an entire core dump.

we have 12gb of ram and setup a 12gb swap partition.  since our
internal disk are for os only and hold no data, this is not an issue.  

what sun recommended in the sysadm classes is to create a smaller swap
partition.  if more space is needed, a swap file can be created.

also, sun now recommends only "/" and swap partitions.  following this
recommendation, a large amount of the "/" partition will be unused;
there will be plenty of room for a swap file.
Kevin Buterbaugh has this to add:
You're right, the old rules about swap no longer apply.  As long as 
you have sufficient physical memory for your peak workload, you can 
actually run with no swap whatsoever configured.  However, that's 
generally not recommended, mainly because in the (rare) event of a system 
panic, it will want to dump to the swap space.

     How much swap you should configure really depends on the application 
you're going to run on the server and its' requirements.  We generally 
configure swap = RAM on our smaller ( < 16 GB RAM) boxes.  For larger 
boxes, it's more like swap = RAM / 2.  YMMV...

thanks for all of the replies and here is my original POST:
Kirk Gilliam
Hello --

I have searched the archives and I still have not found an answer. I have
three V440's with four 1.28GHZ processors and 16 GB of RAM and four 32 GB
disks. The old Sun way for configuring the swap partition was to configure
the partition for one to two times the physical memory. Since memory and
disk are getting cheaper, what is the new rule of thumb? Should I give the
swap partition a 1 to 1 relation which would be a 16 GB swap partition? That
sure seems like a lot of wasted space. What problems would I run into if I
made the swap partition 8 GB or 4 GB. What if I had one 36 GB disk and 32 GB
of RAM, you would not make swap 32 GB, would you?


I will summarize,

Kirk Gilliam
sunmanagers mailing list
Received on Thu Jan 22 12:48:41 2004

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