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Hyper V , Centos 64 bit does not see more then 3Gb Ram

Hi
We have a Hyper V 2008 .

it does not have Hyper Thread enabled

When i am installing a Centos 64 bit and tryign to give it 5Gb of ram, it only see 3GB Ram ...

but with Windows 7, it can see more then 3GB of ram

why Centos does not more then 3Gb ram ??

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fosiul01
Asked:
fosiul01
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1 Solution
 
Kerem ERSOYPresidentCommented:
Hi,

It seems that your CentOS is not actually an 64 bit version. Ae you sure that it is 64 bit distro?? Please try yo redownload an 64 bit version. It should correctly detect the RAM.

Cheers,
K.
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fosiul01Author Commented:
yes, its 64bit version ..

I made sure it was
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Which distro iso did you download?
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fosiul01Author Commented:
its Centos 64 bit

 2.6.18-238.el5 #1 SMP Thu Jan 13 15:51:15 EST 2011 x86_64 x86_64 x86_64 GNU/Linux
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Does it have x86_64 in the filename?
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fosiul01Author Commented:
then uname is showing its 64bit..

how ever its the file name


CentOS-5.6-x86_64-bin-1of8.iso
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Kerem ERSOYPresidentCommented:
Will you check the root directory of DVD and make sure that /CentOS folder contains filesets with x86_64 extension ?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Boot the VM from a Centos x86_64 LiveCDROM, does it show 5GB?
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fosiul01Author Commented:
all of them has both

64 bit and 32 bit extenstion....

and uname -a out put shows that its 64 bit ..
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fosiul01Author Commented:
example

when i install httpd

its shows its getting 64bit rpm


================================================================================
 Package        Arch          Version                      Repository      Size
================================================================================
Installing:
 httpd          x86_64       2.2.3-45.el5.centos.1        updates        1.2 M
Installing for dependencies:
 mailcap        noarch        2.1.23-1.fc6                 base            14 k

so no doubts its a  64bit ..
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fosiul01Author Commented:
@hanccocka

i can try downloading with Centos Live

but i know it would make any difference

because

i have few server which has 64bit but no Hyper thread

in  those case, i could of installed only 32 bit guest ( Debian, Cenetos)


but thsi hyper V, it allow me to install 64bit but will not give more then 3Gb for Centos .

thats why i am confused.... is there anything i need to do on hyper -v as i am nto windows guy .


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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
If you could not installed 64 bit OS, that's because the server has no Intel-VT or AMD-V, Hyperthreading is a different function of the processor.

You may wish to try booting the Windows 7 VM, you have created from the Centos 64bit LIveCDROM does it show all the memory allocated.

What VM type did you use to setup the VM?
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fosiul01Author Commented:
its Hyper V 2008 on Windows 2008 Server.


as i said, Windows 7 can see more then 3GB of ram
but not cenetos

i am downloding Centos Live Cd, see what it shows
i will come back to you .

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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Yes, I understand, but to isolate if it's a VM setup, issue, if you boot the x64 Centos LiveCDROM on the Windows 7 VM and it "sees" more than 3GB, but booting on the Centos VM, it does not, it's a VM setup issue.
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fosiul01Author Commented:
what you meant by

boot the x64 Centos LiveCDROM on the Windows 7 VM  ??

is not same , that create a seperate a vm, then boot that one with Live Cd ??
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Use the CDROM to boot both VMs (Windows 7 and Centos), and check memory.
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fosiul01Author Commented:
with live cd enabled , its stiill 3Gb ram

have a look at picture
livecentos.GIF
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
if you boot the Windows 7 VM?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
can you screenshot the VM settings?
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fosiul01Author Commented:
if i boot the windows 7 VM its same thing

here is the setting


win7.GIF
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Can you increase the memory in the VM, to beyond 4096?

e.g. 5120MB

How much memory do you have in the Hyper-V host?
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fosiul01Author Commented:
yes, i tryed with 5000 to 6000 Gb

i can increase ..

it has only 1 vm

yesterday, i shut all vm down.. and gave it 6000 , still its shows bellow 3GB

then Hyper-V host has 8 Gb ram
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Your Hyper-V host does not have much memory. Hyper-V does not support memory over commit as does VMware ESXi, e.g. the ability to give VMs memory, that your host does not physically have.
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fosiul01Author Commented:
then how windows 7 getting 4Gb of ram ??
 
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
What is Windows reporting?

4096M?

You Centos Installation is reporting 3834M on the same VM, that's above 3GB.

If you set the VM to 5120MB, what does Windows and Centos report?|
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fosiul01Author Commented:
yes
windows reporting 4096M

so Centos should report 4096 is not it ??

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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
when you set the VM to 5120M what does Windows and Centos report?
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fosiul01Author Commented:
i cant set that one to 5120 as there is another vm is runing, i can only shutdown  at n ight

but yesterday at night

i gave centos more then 5gb and only centos was runing on that host

still it was showing 3GB
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
try dmesg|more

and search for the line similar to this

Memory: 6226304k/7340032k available

when using 64 bit or PAE mode, not all the memory may show in the above example 8GB is in the server (physical).

Do you need to use more than 4GB of memory for your Centos VM?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
shut down all the VMs, and try setting 5120MB, and use dmesg|more
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fosiul01Author Commented:
have a look windows 7 booted with 5GB ram

so hyver -V does allwo 5Gb for windows 7
windows7-5gb.GIF
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
what does dmesg? state?
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fosiul01Author Commented:
just boot the centos


dmesg | grep memory
Freeing initrd memory: 3438k freed
Total HugeTLB memory allocated, 0
Non-volatile memory driver v1.2
Freeing unused kernel memory: 224k freed


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fosiul01Author Commented:
with Windows  2008 R2 hyper -V , its see more then 3GB of ram

but normal windows 2008 Hypver -V, its looks odd

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fosiul01Author Commented:
ok debian live 64 bit see more then 3GB

so its something to do with Centos !!!!

never seen this prolem

at least I now where to look for ..
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
I normally get a line like this

Memory: 6226304k/7340032k available (1876k kernel code, 63668k reserved, 759k data, 184k init, 5373376k highmem)
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fosiul01Author Commented:
is there  anything in bios setup of vm ??

ref : http://blogs.msdn.com/b/hiltonl/archive/2007/04/13/the-3gb-not-4gb-ram-problem.aspx


1. Can Windows access memory above 4GB?

    a. 32-bit – NO

    b. 64-bit – Maybe (due to chipset limitations)

2. Can your processor access memory above 4GB?

    a. If it’s recent then it might, and if it’s either AMD64 or EM64T it’s almost certain

note debian kernel is AMD64 ..
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fosiul01Author Commented:
do you know how to view bios setting of VMs ??

i just wanted to see how much ram in bios on Centos vm
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
The Hyper-V virtual machine BIOS settings are limited to selecting the device from which the guest operating system is to be loaded from when the virtual machine is powered on and choosing whether or not the Num Lock key is on by default:

It's not like a VMware VM!
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