swapoff paging space 2

[MoreFeo]

Hi, we have some servers with more than one paging space in a disk (hd6 mirrored in hdisk0 and hdisk1, and another paging00 not mirrored in hdisk1).
We've been told that more than one paging space on a disk (in our case hdisk0) can impact on performance, so we're thinking about increasing hd6 and removing the other.
This is what we are planning to do:
- increase hd6
- swapoff paging00
- rmps paging00

I've read that during swapoff it moves all allocated pages in paging00 to hd6 (that seems logical), so I wanted to know if this can affect in any way on our servers performance and running applications (oracle, websphere, etc...).

Thanks

 

[RodKnowlton]

What's the current paging space utilization (lsps -a)?

- Rod


IBM Certified Advanced Technical Expert pSeries and AIX 5L
CompTIA Linux+
CompTIA Security+

Wish you could view posts with a fixed font? Got Firefox & Greasemonkey? Give yourself the option.

 

[khalidaaa]

IMHO why do you need to have the hd6 mirrored? I think you should better use paging00 on hdisk1 and hd6 on hdisk0!

after you know what Rod is said above about the paging utilization.

If you don't need two paging spaces then you can go ahead and remove the paging00!


Regards,
Khalid

 

[khalidaaa]

I would like to share with you this link:

http://unix.derkeiler.com/Mailing-Lists/AIX-L/2003-11/0276.html

Regards,
Khalid

 

[MoreFeo]

Rod, in most of the servers lsps -a shows about 10 and 25 %Used for hd6 and paging00 (depends on the server they are 1 GB to 4 GB).
But there is one server with more PS (hd6 4 GB and paging00 10 GB) that sometimes has more than 90 %Used in each paging space (we need to fix this, but it's not in production so we don't hurry as much). Right now this server has only around 2 o3 %Used.

Khalid, I also used to think that its better a PS on hdisk0 and another on hdisk1, but I've been told that if hd6 is only on one disk (lets say hdisk0), if hdisk0 crashes all the apps that were using hd6 cannot continue and it crashes (so no benefit of having rootvg mirrored if hd6 is not).

 

[p5wizard]

IMHO why do you need to have the hd6 mirrored? I think you should better use paging00 on hdisk1 and hd6 on hdisk0!

[soapbox mode]
If you mirror rootvg, you need to mirror all LVs in rootvg (except dumplv which mustn't be mirrored, but you can have two of them: primary and secondary dump device).
If a "mirror"-disk of rootvg fails and it contains the only copy of one of your swapspaces, the server WILL HALT.
[/soapbox mode]



HTH,

p5wizard

 

[khalidaaa]

Thanks for the clarification p5wizard!

 

[RodKnowlton]

A star for p5wizard both for the post, and for using TGML for his fake markup.

- Rod

 

[MoreFeo]

p5wizard, that's exactly what I was told. And does anyone know if swapping off a paging space can impact on running applications or performance?

 

[p5wizard]

I don't know if it has a big impact, but I've seen it take quite a while to swapoff a paging space.

But you didn't answer Rod's question: what is the % in use of the paging sapce you want to swapoff?


HTH,

p5wizard

 

[MoreFeo]

Well, as I said in all servers it's around 10 and 25 %Used of paging spaces 1 GB to 4 GB size, except for a server where it can grow sometimes up to more than 90 % of a 4 GB and a 10 GB PS.

 

[p5wizard]

If you have a paging space that's 25% used, and there's enough room in your other paging space(s) to hold the pages while you're swapoff-ing it, until you've freed enough diskspace to increase the other paging space(s), you should be fine.

I would do an operation like this in off-peak time though.


HTH,

p5wizard

 

[MoreFeo]

Thanks a lot, we'll do it one night, when the server is supposed to be less active.

 

[p5wizard]

Gee, thanks for all the nice purple stars guys...

p5wizard

 

[cts123]

p5wizard and Khalida,

Thanks to both of you for this tip. I want to include one more thing at this time, which I have.

My SAP AIX server is having AIX 4.3.3 and due to some internal reason, we can't upgrade that machine to AIX 5.3

At this point of time, if I do lsvg -l rootvg its showing :-

$ lsvg -l rootvg
rootvg:
LV NAME TYPE LPs PPs PVs LV STATE MOUNT POINT
hd5 boot 1 2 2 closed/syncd N/A
hd6 paging 250 250 1 open/syncd N/A
hd8 jfslog 1 2 2 open/syncd N/A
hd4 jfs 4 8 2 open/syncd /
hd2 jfs 212 424 2 open/syncd /usr
hd9var jfs 14 28 2 open/syncd /var
hd3 jfs 39 78 2 open/syncd /tmp
hd1 jfs 3 6 2 open/syncd /home
paging00 paging 250 250 1 open/syncd N/A
lv00 jfs 16 32 2 open/syncd /u01

Only hd6 and paging00 are w/o mirrored and they are in two different disk. which is :-


$ lsps -a
Page Space Physical Volume Volume Group Size %Used Active Auto Type
paging00 hdisk1 rootvg 4000MB 16 yes yes lv
hd6 hdisk0 rootvg 4000MB 16 yes yes lv


hdisk0 = hd6
hdisk1 = paging00

And I don't have any space left in the rootvg to make it mirror.

$ lsvg -p rootvg
rootvg:
PV_NAME PV STATE TOTAL PPs FREE PPs FREE DISTRIBUTION
hdisk0 active 542 2 00..00..00..00..02
hdisk1 active 542 2 00..00..00..00..02


If tomorrow my hdisk0 fails, even if my all LVs are mirrored, my system won't boot. Correct ?

So, you mean at that time, do I need to swap paging00 to hd6 to make the machine working? Do I need to follow the URL which Khalida addressed ?

http://unix.derkeiler.com/Mailing-Lists/AIX-L/2003-11/0276.html

I have to boot the machine with AIX media, and get shell and modify the file /sbin/rc.boot to make paging00 as hd6 ?

-Correct me if I am wrong.

At this point of time, I don't have any option left. Client doesn't want to add any disk, since the machine is very old. And I don't have any PP left in rootvg, to make it mirrored the hd6.

TIA ..

 

[RodKnowlton]

Remove paging00, then mirror hd6 with the PP you've freed.



IBM Certified Advanced Technical Expert pSeries and AIX 5L
CompTIA Linux+
CompTIA Security+

Wish you could view posts with a fixed font? Got Firefox & Greasemonkey? Give yourself the option.

 

[p5wizard]

If you loose paging00, your system will halt but will reboot
If you loose hd6, your system will halt and won't reboot because hd6 is gone - as you stated: you then need to go to maint boot from install media, access rootvg, rename paging00 to hd6 (chlv -n hd6 paging00), cross fingers, burn incense sticks, pray to your deity... and boot


How to get rid of this single point of failure:

Trouble is, if you need that much paging space, you can't do it in rootvg alone.

If you have free space in other VG, then you can:

- reboot with paging00 not auto active (there's no swapoff in AIX433)
- remove paging00
- mirror hd6 on freed space
- create new paging00 on other (mirrored)

see "smit paging" for more info.


HTH,

p5wizard

 

[cts123]

p5wizard,

I don't have any VG available where I can find some space!!

$ for i in `lsvg`
> do
> lsvg -p $i
> done
rootvg:
PV_NAME PV STATE TOTAL PPs FREE PPs FREE DISTRIBUTION
hdisk0 active 542 2 00..00..00..00..02
hdisk1 active 542 2 00..00..00..00..02
raid_vg1:
PV_NAME PV STATE TOTAL PPs FREE PPs FREE DISTRIBUTION
hdisk2 active 3258 0 00..00..00..00..00
hdisk3 active 3258 0 00..00..00..00..00
raid_vg2:
PV_NAME PV STATE TOTAL PPs FREE PPs FREE DISTRIBUTION
hdisk4 active 3258 0 00..00..00..00..00
hdisk5 active 3258 0 00..00..00..00..00
raid_vg3:
PV_NAME PV STATE TOTAL PPs FREE PPs FREE DISTRIBUTION
hdisk6 active 3258 0 00..00..00..00..00
hdisk7 active 3258 0 00..00..00..00..00
raid_vg5:
PV_NAME PV STATE TOTAL PPs FREE PPs FREE DISTRIBUTION
hdisk9 active 3258 2 00..00..00..00..02
hdisk10 active 3258 0 00..00..00..00..00
raid_vg6:
PV_NAME PV STATE TOTAL PPs FREE PPs FREE DISTRIBUTION
hdisk11 active 3258 0 00..00..00..00..00
hdisk12 active 3258 1 00..00..00..00..01

The Physical memory of the server is 6GB. And I believe to match the physical memory with paging space, previous admin guy made 8GB paging space ( 4GB in two diff. disk w/o mirror).

P5wizard, I believe thats the only way which you mentioned in case of hd6 failure, cross fingers, burn incense sticks, pray to your deity... and boot afer renaming paging00 to hd6

Is my 4GB of paging space not sufficient for use? If we findout that 4GB is pretty much ok with respect to 6GB physical memory, I can follow RodKnowlton's advise. Right ?

 

[p5wizard]

Q1: Right AND...

Get your customer to agree with this single point of failure!

Q2: If you can make do with 4GB paging space, go for Rod's advice.


Tip: there's a shortcut for your loop:

lsvg|lsvg -ip

or better yet (only varied on VGs)

lsvg -o|lsvg -ip

Thsi works with "-il" flags also (LV info per varied on VG) or without extra flag "-i" for details of all varied on VGs


HTH,

p5wizard

 

[khalidaaa]

I just found this link on the net while surfing! But i still see what p5wizard and Rod saying is logical!

Good point to raise cts123.

Regards,
Khalid