Swap space

[Stafford Hyacinth]

The HP docs indicate "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."

I have a system with 32GB physical ram
and 16GB swap. Is it recommended that I increase the swap space to 32GB?
Thanks

[Alan Meyer_4]

Check out this recent thread for swap recomendations
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=941041

[RAC_1]

Your just fine. 16gb will suffice. Have you set swapmem_on to 1?? IF not, you should be.
Turning this on will result in swap space calculted as follows
swap space configured + 75% of RAM.

(This is just for kernel calculation)

You should be worrying about dump space.

Anil

[DCE]

As long as the kernel parameter swapmem_on is set to 1 you are fine. This parameter activates psudeoswap which is ideal for use on large memory systems such as yours

[Geoff Wild]

This really depends on your application(s)...

For example, if you were running SAP - you would need about 24GB swap.....regardless of the ammount of ram...



Rgds...Geoff

[A. Clay Stephenson]

Even with SAP the only time you need large amounts of swap is during installation. You can even use the dreadful, slow filesystem swap for SAP installation and then remove it. After installation, the swap isn't needed. It's actually not even needed during installation but the installation procedure checks for the amount of swap and fails otherwise. In your case, you could probably get by with 8GB of swap and set swapmem_on=1.

[Basheer_2]

Hi Stafford

is your system swapping (if swapinfo -tm will show PCT USED for dev > 0)

if so then there is a procedure to create secondary swap

[Stafford Hyacinth]

Thanks everyone. Below is the result of a swapinfo. Also can someone pls let me know how the point system works, I don't want to short change anyone.

nhsbpdb1# swapinfo -tm
Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 4096 0 4096 0% 0 - 1 /dev/vg00/lvol2
dev 4096 0 4096 0% 0 - 1 /dev/vg00/swap2
dev 4096 0 4096 0% 0 - 1 /dev/vg00/swap3
dev 4096 0 4096 0% 0 - 1 /dev/vg00/swap4
reserve - 12249 -12249
total 16384 12249 4135 75% - 0 -

[Alan Meyer_4]

Check here to find out about points

http://forums1.itrc.hp.com/service/forums/helptips.do?#35

[A. Clay Stephenson · Accepted solution]

Okay, you do have a problem. It appears that you do not have the kernel tunable swapmem_on set to 1 because I do not see a "memory" line in your swapinfo output. You can confirm this by running "kmtune -q swapmem_on". Yours will indicate 0. In that case, you will only be able to run 16GB's of processes. You need to A) increase the swapspace to 32GB or B) better, set swapmem_on=1 and build a new kernel. This will then allow you to use your full 32GB of memory because now the systems pretends that it's total virtual space is 0.75 X RAM + actual swap space.

[Kent Ostby]

Stafford --

As you can probably tell from the various replies that this really depends on your applications.

In general, I've seen system's hang that have less than 2xRAM in device swap and heavy oracle users needing as much as 3xRAM.

I would suggest that you move up to 1x personally to start with and then check your performance as you go.

Also, check to ensure that you will capture a full crash dump, by looking at the output from crashconf -v .

[Stafford Hyacinth]

Thanks all for the timely responses. I am going to change "swapmem_on" to 1 and not increase swap for now.