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

Posted on 2011-09-05
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Last Modified: 2012-05-12
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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Question by:fosiul01
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Expert Comment

by:Kerem ERSOY
ID: 36483369
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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Author Comment

by:fosiul01
ID: 36483376
yes, its 64bit version ..

I made sure it was
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LVL 117
ID: 36483397
Which distro iso did you download?
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Author Comment

by:fosiul01
ID: 36483400
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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LVL 117
ID: 36483401
Does it have x86_64 in the filename?
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Author Comment

by:fosiul01
ID: 36483407
then uname is showing its 64bit..

how ever its the file name


CentOS-5.6-x86_64-bin-1of8.iso
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Expert Comment

by:Kerem ERSOY
ID: 36483411
Will you check the root directory of DVD and make sure that /CentOS folder contains filesets with x86_64 extension ?
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LVL 117
ID: 36483418
Boot the VM from a Centos x86_64 LiveCDROM, does it show 5GB?
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Author Comment

by:fosiul01
ID: 36483421
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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Author Comment

by:fosiul01
ID: 36483424
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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Author Comment

by:fosiul01
ID: 36483441
@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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LVL 117
ID: 36483451
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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Author Comment

by:fosiul01
ID: 36483469
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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LVL 117
ID: 36483518
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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by:fosiul01
ID: 36483526
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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LVL 117
ID: 36483561
Use the CDROM to boot both VMs (Windows 7 and Centos), and check memory.
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Author Comment

by:fosiul01
ID: 36483603
with live cd enabled , its stiill 3Gb ram

have a look at picture
livecentos.GIF
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LVL 117
ID: 36483629
if you boot the Windows 7 VM?
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LVL 117
ID: 36483632
can you screenshot the VM settings?
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Author Comment

by:fosiul01
ID: 36483667
if i boot the windows 7 VM its same thing

here is the setting


win7.GIF
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LVL 117
ID: 36483699
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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Author Comment

by:fosiul01
ID: 36483705
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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LVL 117
ID: 36483718
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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Author Comment

by:fosiul01
ID: 36483725
then how windows 7 getting 4Gb of ram ??
 
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LVL 117
ID: 36483768
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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Author Comment

by:fosiul01
ID: 36483842
yes
windows reporting 4096M

so Centos should report 4096 is not it ??

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LVL 117
ID: 36483857
when you set the VM to 5120M what does Windows and Centos report?
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Author Comment

by:fosiul01
ID: 36483875
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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LVL 117
ID: 36483879
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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LVL 117
ID: 36483888
shut down all the VMs, and try setting 5120MB, and use dmesg|more
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Author Comment

by:fosiul01
ID: 36483895
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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LVL 117
ID: 36483903
what does dmesg? state?
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Author Comment

by:fosiul01
ID: 36483910
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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Author Comment

by:fosiul01
ID: 36483975
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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Author Comment

by:fosiul01
ID: 36484028
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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LVL 117
ID: 36484047
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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Author Comment

by:fosiul01
ID: 36484074
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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Author Comment

by:fosiul01
ID: 36484284
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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Accepted Solution

by:
Andrew Hancock (VMware vExpert / EE MVE) earned 500 total points
ID: 36484302
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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