Swap information

[Gordon_3]

Hi all,

Most of our unix machines shows below typical swap information, i.e. It only use memory swap but not device swap, so just wanna know is it a healthy setting? I seldom see any of my machines use the device swap, is it because I tune up the memory swap too large? Thx.

Gordon

Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 1024 0 1024 0% 0 - 1 /dev/vg00/lvol2
dev 3072 0 3072 0% 0 - 1 /dev/vg00/swap2
dev 4312 0 4312 0% 0 - 1 /dev/ip1emc4/swap3
dev 4312 0 4312 0% 0 - 1 /dev/ip1emc4/swap4
reserve - 4869 -4869
memory 7133 5139 1994 72%
total 19853 10008 9845 50% - 0 -

[Michael Tully · Accepted solution]

Hi Gordon,

Depending on your application(s) as to whether you require additional swap these days.
How much is your buffer cache setting? If it is default (dbc_max_pct=50), then it is too high.
Have a look at glance, this will tell you how much memory V's buffer cache and swap is being used.
As an example I have a system, where I have 8Gb RAM and only 2Gb swap, dbc_max_pct=7

If your still unsure, please post:
swap usage from glance
memory usages from glance and the buffer cache usage
buffer cache value from your kernel

Regards
Michael

[Gordon_3]

Hi Michael,

I only set 20% for the dbc_max_pct, as so far it's mostly recommend in this forum. My glance info show below. I do still have free memory. So is below figure healthy?

Gordon


Total VM : 517.4mb Sys Mem : 453.8mb User Mem: 5.45gb Phys Mem: 9.00gb
Active VM: 398.3mb Buf Cache: 752.5mb Free Mem: 2.37gb

[Michael Tully]

Hi Gordon,

The actual buffer cache recommendation is betwen 300-500Mb.
Other than fixing that at a conventient time, I don't see any other real problems. If anything, you may wish to remove some of the swap (also at a later time) if you ever need to re-claim some disk space.
The two swap areas on /dev/vg00, are they on the same disk? You should try to have your swap elsewhere and not on the same internal disk, except for enough swap to boot the system. Changing the swap priorities to external disk is easy and can be done in your /etc/fstab file.

HTH
Michael

[Gordon_3]

Hi Michael,

Can u share with me how to do the changing priority in /etc/fstab ? Thx.

Gordon

[Michael Tully]

Hi Gordon,

Your primary swap on your server will be priority 1
The entries in your /etc/fstab file should be like this. The idea is to give high or equal priority to other swap devices once the system boots.

/dev/apps/swap1 ... swap pri=1 0 0

I've attached a document on memory management which can be found on HPUX 11 systems, that should prove useful. It is quite generalised and is not installed on 11i.

HTH
Michael