SWAP Info

[Marvin L. Diaz]

Hi Guys,

I have encountered a HPUX system in which the swap is in a mounted file system.

Is there any bad implication of this?

Kb Kb Kb PCT START/ Kb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 8388608 7479476 909132 89% 0 - 1 /dev/vg00/lvol2
localfs 20971520 0 20971520 0% 20971520 0 1 /swap/paging
reserve - 19618900 -19618900
memory 8386560 1874708 6511852 22%


when i do the "bdf" the /swap/paging is moun ted.

[TY 007]

Hello Marvin,

Best if able to use Device Swap such as /dev/vg00/lvol2.

If no choice, filesystem swap should be fine.

If there is enough disk space for additional Device Swap, do consider it :)

Thanks

[Marvin L. Diaz]

TY,

What i am asking that, is it okay that the swap is visible on the "bdf" command.

i know lvol2 swap. the server is running SAP

[whiteknight]

Mavin,

No issue. Make sure you have any entry in /etc/fstab, so that when you reboot next time it will be automatically mounted

WK

[Marvin L. Diaz]

what about the I/O impact?
i tried to get into that directory /swap.

i found out that there are files located into it.

is that ok?

many thanks

[TY 007]

Hello Marvin,

>> what about the I/O impact?

If possible, /swap/paging should not be located in Boot Disk or /dev/vg00

The impact depends whether Application requires heavy swapping :)

Thanks

[whiteknight]

Marvin,

filesystem swap will have high i/o impact than device swap.

We usually recommend customer use device swap

WK

[Marvin L. Diaz]

Hi WK,

Do have a document with regards to what you have mention?

Cheers

[whiteknight]

Hi Marvin,

Make sure you have valid HP support contract linked to itrc.

http://www2.itrc.hp.com/service/cki/docDisplay.do?docLocale=en&docId=emr_na-c00904894-7

WK

[Marvin L. Diaz]

Hi WK,

I would appriciate if you can send me a copy for that. I cannot access the site you send. It need a maintenance aggrement login.

Cheers

[whiteknight · Accepted solution]

Marvin

I cut and paste the differece between 2 type of swap space

WK

[Enrico P.]

Hi,
I hope this help you:

http://www.docs.hp.com/en/B2355-90950/ch06s03.html#d0e54987

Enrico

[A. Clay Stephenson]

There is really nothing wrong with filesystem swap (and yes, it is worse on performance than device swap but Big Woo!). Note that the priority of both your device swap and filesystem swap is set to 1. You normally want to set filesystem swap to a lower swap priority (higher number) so that it will be used later. I would modify the /etc/fstab entry to set the priority to 5 or so.

Now back to Big Woo: Using device swap, the performance impact of significant swapping is perhaps 100X worse compared to not swapping. For filesystem swapping this might rise to 110X worse. For both the performance impact is so bad that the differences are really not worth worrying about. This is truly a case of rearranging the deck chairs on the Titanic.

[Marvin L. Diaz]

Thanks all for your help.

cheers!!!