SWAP area management

[Enrico Venturi]

Hello colleagues.
We've to manage a server and our system administrator can't do it since he resigned last month.
The server is equipped with 16 GByte of RAM.
We found the swap area is 16 GByte on disk:
is it enough? what's the rule to choose the swap area?

If it isn't enough we should increase it, isn't it?
How can we do it?

thanks for the support

Enrico

[Peter Godron · Accepted solution]

Enrico,
there are no definite rules about how much swap you need, some depends on what sort of application you are running, how many users you have etc.

My, personal, 'rule' is to allow 1.5 times the amount of physical memeory.
You can always monitor the machine, and then allocate more if needed.

As you don't have a Sys. Admin, I would suggest you use System Admin Module (SAM), the HP graphical interface for admin tasks.

See "man sam" for help.

[Ivan Krastev]

See this doc about "Managing Swap and Dump" - http://docs.hp.com/en/B2355-90950/ch06s03.html

regards,
ivan

[Eric Antunes]

Hi Enrico,

You must monitor it to see if it is enought (use "swapinfo -tam" command). Also check page outs with "vmstat -nS 3 99999"...

Thank you,

Eric Antunes

[Reshma Malusare]

Hi Venturi,
1. Available swap on a system consists of all swap space enabled as device and file system swap. To find how much swap space is presently available on your system and how much is being used, use SAM or run the command swapinfo.
2.Estimating Your Swap Space Needs
Your swap space must be large enough to hold all the processes that could be running at your system's peak usage times.

If your system performance is good, and, in particular, if you are not getting swap errors such as Out of Memory or those to the effect that a process was killed due to no swap space, then your system has adequate swap space.

Typically, unless the amount of physical memory on your system is extremely large, the minimum amount of swap space should equal the amount of physical memory on the system. Generally, a rule of thumb is to make swap space to be roughly two to four times your physical memory.
Swap space usage increases with system load. If you are adding (or removing) a large number of additional users or applications, you will need to re-evaluate your swap space needs.

If you want go for following calculation:

Local Swap Space Needs
-->For standalone (a server or otherwise) and client systems that will swap to local swap space either to a device or a file system, you can estimate your swap space needs as follows:

1. Enter the amount of the physical memory currently on the local machine. At a minimum, swap space should equal that amount. Enter the amount in KBs.

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2. Determine the swap space required by your largest application (look in the manual supplied with your application or check with the manufacturer; 1MB = 1,024KBs = 10,248 bytes). If you will be running several applications concurrently, you should add their swap space requirements
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TOTAL local swap space needed (in KBs): sum of 1 & 2
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--> Server Swap Space Needs
For a system that has local swap and also serves other systems with swap space, make a second estimation in addition to the one above.

1. Include the local swap space requirements for the server machine, based on the estimation from above.

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2. Add up the total swap space you estimate each client requires. At a minimum, this number should equal the sum of physical memory for each client.

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TOTAL server swap space (in KBs):sum of 1 and 2



Regards
Reshma