Originally posted by: amitmacau

I want to configure a VG of size 900GB with 25 disks of 36GB each. Is it possible. What would be the PP size.
As per my knowledge for adressing 36 GB in AIX 5.2 , PP size should be 64MB ie Volume Multiplier factor of 16. So the limit of Big VG of 128 Hard disks /16= 8 disks. That implies with 36 Gb hard disk I can only have maxm VG as ( 36 * 8 = 288GB )288Gb only.

Pls suggest.

Originally posted by: HajoEhlers

From my knowledge the maximum amount of disks per vg is 32 ( except big VGs)

You have 25 disks > I see no problem

Normaly you have 1016 PP per PV ( hdisk) meaning on a 36GB disk the pp size should be at least 64 ( I would go for 128 or even 256 ) -> I see no problem

So in case you are using a PP size of 64 you will have total of 576 PVs per disk and a total of 25*576=14440 PPs.
I do not know if there is a limit or what the limit is for "TOTAL PPs:"

At least i found a post on c.u.a that stated 11319 PPs so what is your problem ?

So the only concern is the PP size in case you would like to add bigger disks to the VG. For that reason i would go for a PP Size of 256 MB because who know how long you get a equaly 36GB disk replacement

regards
Hajo

Originally posted by: amitmacau

Thanks for your mail.

I put my question other way. I want to have a VG of 900GB, with 25 number of 36 GB hard disks ( disks will be assigned from SAN ). Is it possible. If yes what should be the PP size. Or pls let me know the excat command to do the above mentioned.

Regards

Originally posted by: HajoEhlers

>
> I put my question other way. I want to have a VG of
> 900GB, with 25 number of 36 GB hard disks ( disks
> will be assigned from SAN ). Is it possible.

imho - yes . If it makes sense to have 25 small disk via a san is a different story.

> If yes
> what should be the PP size.

Have you read my post ? The lowest PP size is 64 MB. If you use a PP size of 64MB you are stucked with that disk size. So i would go for 256MB which means a maximum disk size of 260 GB.

> Or pls let me know the
> excat command to do the above mentioned.

1. With a PP size of 256MB

$ mkvg -s 256 -y newvg hdiskN hdiskN+1 .. hdiskN+25

In case you need a big vg see - man mkvg - for details

$ man mkvg
$ man extendvg
$ smitty mkvg

hth
Hajo

Originally posted by: amitmacau

mkvg -s 256 -y newvg hdiskN hdiskN+1 .. hdiskN+25

with this command, the PP size is 256. To increase the PP size the size of t factor would also increase and which reduce the number of Hard Disks possible.

With PP size of 64 the t factor would be 16 ( t factor would further increase if i increase the size of PP ).

Number of Maxm Hard Disks in Big VG= 128/t factor

In our case Maxm Hard Disks possible = 128/16=8.

So 36Gb size Hard Disk * 8= 288GB. So logically I can have only 288GB size VG.

Pls correct me if I am wrong.

I need VG of 900GB with 36GB Hard Disk.

Originally posted by: HajoEhlers

Please read the man pages for mkvg regarding the " - t" option. I think you have a missunderstandung of what the " -t " is for. So for the last time:

A disk no matter how big can hold by default 1016 PPs. Punkt!
Now a PP has a certain size between 2,4,8,16,32,256,512 and 1024 MB

What does that mean:
If your PP size is 8MB, the maximum physical disk which can be used is: 8124MB
If your PP size is 256MB, the ... is: ~250 GB
At this point we never ever talked about the -t option because it was simple not nesseccary.

So what is the use of the -t option:
If you have an old RS/6000 with a 4GB disk the installation normaly set a default PP size of 4MB. This was 5 years ago. Now you would like to add a new disk to your rootvg which has a size of 36GB.

If you followed until here you should be able to realize that this disk can not be added to a vg with a pp size of 4MB. A 36GB disk need a pp size of at least 64 MB. That is a mess. So IBM made a fix where you lower the number of possible disk in a VG but increasing the total amount of PP per disks.

In our above example we need for a 36 GB - which shall be added to a VG - with a pp size of 4MB round about 10000 PP.
This means we need to change the number of possible disk in that VG down to ...
Disks - Total PPs
16 - 2032
8 - 4064
4 - 8128
2 - 16256

... down to 2 Disk.
So after adding this 36GB to an existing VG with an pp size of 4MB it is NOT possible to add further disk to the VG.
Another examaple:
The san people assign a 1200GB disk to you . Even with a pp size of 1024 you can not reach that size ( 1016*1024 < 1200 ). But if you reduce the maximum ammount of disk by 1/2 your MAX PP for PV will increase to 2032 thus that big disk can be used.
So its IMPORTANT in the beginning of a volume group creation to select a proper PP size in case larger disk shall be added to the VG in the future. For this reason all my AIX installation starting with a PP Size of 256 MB. ( The size a JFS logs normaly needs )

The reason why in the older days no larger PP has been used is simply that each LV uses at least ONE PP. So on a 2GB disk with an PP size of 256MB you could have a maximum of 8 LV.
Hajo

Originally posted by: amitmacau

Thanks...i was confusing with t factor.....
Thanks a ton
Regards
Amit