Linux-PowerEdge digest, Vol 2 #338 - 4 msgs

Anthony_Doyle@Dell.com Anthony_Doyle at Dell.com
Tue Jun 24 06:26:01 CDT 2003


As per the redhat customization guide "if you have a computer with more than
four gigabytes of memory, you need the kernel -bibmem package.
It is reccommended to install this package for debugging purposes.
The kernel -bigmem package is ony built for the i686 architecture"
see
http://www.redhat.com/docs/manuals/linux/RHL-9-Manual/custom-guide/s1-kernel
-preparing.html

This is a limitation of a 32-bit architecture. The system can only address 4
GB of allocated memory. Allocated memory is made up of physical ram, and any
I/O space needed by devices. The way memory is allocated is that starting at
4GB the system allocated device I/O addresses working it's way down. 

-----Original Message-----
From: linux-poweredge-request at dell.com
[mailto:linux-poweredge-request at dell.com]
Sent: 24 June 2003 12:00
To: linux-poweredge at dell.com
Subject: Linux-PowerEdge digest, Vol 2 #338 - 4 msgs


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Today's Topics:

   1. PERC 3/QC and memory usage ... (Alan Bunch)
   2. Re: PERC 3/QC and memory usage ... (Paul)
   3. RE: PERC 3/QC and memory usage ... (Stig_Fjeldheim at Dell.com)
   4. Re: PERC 3/QC and memory usage ... (Mark Watts)

--__--__--

Message: 1
Subject: PERC 3/QC and memory usage ...
From: Alan Bunch <alabun at spyderinc.com>
To: linux-poweredge at dell.com
Organization: Spyder Enterprises Inc
Date: 23 Jun 2003 23:28:10 -0500

Dear assembled experts ...

PE 2650
4 g ram
PERC 3/QC controler
PERC 3/Di ROMB
Adaptec 39160

RHAS 2.1 @ version e25

Setup says I have 4096 mb of ram

I do not have OS setup mode turned on.

RHAS 2.1 says I have 3.5 g of ram

Memory diags says I have 3.5 g of ram.

Dell support says that each channel on the QC card take 128 mb of ram
explaining the .5 g shortfall in memory.

1. Did I just get the support rep who fell of the truck yesterday to
answer my call and this was the best guess he could come up with to
explain the facts ?

2. If this is in deed the case what does all of that ram get used for ?

3. How could I have known this *BEFORE* I ordered ? Where is it
documented now that I own it ?

Thank in advance,

alabun



--__--__--

Message: 2
From: "Paul" <paul at kbs.net.au>
To: "Alan Bunch" <alabun at spyderinc.com>
Cc: <linux-poweredge at dell.com>
Subject: Re: PERC 3/QC and memory usage ...
Date: Tue, 24 Jun 2003 15:35:31 +1000


I'm going off what I know so here goes..

#1 RHAS 2.1 says I have 3.5 g of ram
The OS should be able to access all of it. This is part of a "highmem" mode
in the kernel. You can try passing it as a kernel option but you shouldn't
need to. It should automatically do this, especially for a new OS such as RH
AS. 32bit Kernels and programs only have access to 3.5GB of memory as the
other 500mb of used for Kernel allocation and other 32bit functions. Any
program (32bit only) including the kernel is only able to access upto 3.5GB.
This is a limitation of the 32bit architecture. 64bit Architecture has
higher adderesssing limts, upto 64GB (not 100% sure??) Again I'm not 100%
sure, this is what I have learnt. Any single process (aka kernel) can only
use 3.5GB at any one time. All programs started after the kenel (aka init)
fall under init itself so they too can only get to 3.5GB of ram.

#2 Memory diags says I have 3.5 g of ram.
This would be because the Kernel suffers the same limitation. If the kernel
can only access 3.5GB then any program under will be the same. This would
also apply for any Dell diags as they are 32bit programs, run via a DOS
shell or shelldos command boot disk or "utiliity" mode partition. These also
have the same memory addressing fallback as it's a 32bit program.

#3 Dell support says that each channel on the QC card take 128 mb of ram
explaining the .5 g shortfall in memory.
The Dell PERC cards have additional memory chips on the motherboard. These
are SDRAM chips @ 133mhz ECC.
Your normal memory would be DDR @ 300+MHZ ECC (at a guess). So what Dell are
telling does not sound correct.
All PERC's I know of have their memory modules on the motherboard seperate
from the system memory.

Well the QC is a quad channel card? Correct? So if you were to boot the
server with 4 x 128mb chips in your main DIMM slots you would essentially
have no ram for the OS?
What happens if you boot the server with 4 x 128mb ECC chips? Does this mean
you boot with 0mb of ram? If what Dell is saying is true that means you
would boot OS (RH AS) with 0mb of ram as Each of those 4 x 128mb chips would
be used by the PERC QC. I'd be suprised if the PERC QC could use DDR instead
of the traditional SDRAM @ 133mhz

Interesting conversation...

Anyone have any excact info?

Hope this helps (dont take all my info 100% correct)

----- Original Message ----- 
From: "Alan Bunch" <alabun at spyderinc.com>
To: <linux-poweredge at dell.com>
Sent: Tuesday, June 24, 2003 2:28 PM
Subject: PERC 3/QC and memory usage ...


> Dear assembled experts ...
>
> PE 2650
> 4 g ram
> PERC 3/QC controler
> PERC 3/Di ROMB
> Adaptec 39160
>
> RHAS 2.1 @ version e25
>
> Setup says I have 4096 mb of ram
>
> I do not have OS setup mode turned on.
>
> RHAS 2.1 says I have 3.5 g of ram
>
> Memory diags says I have 3.5 g of ram.
>
> Dell support says that each channel on the QC card take 128 mb of ram
> explaining the .5 g shortfall in memory.
>
> 1. Did I just get the support rep who fell of the truck yesterday to
> answer my call and this was the best guess he could come up with to
> explain the facts ?
>
> 2. If this is in deed the case what does all of that ram get used for ?
>
> 3. How could I have known this *BEFORE* I ordered ? Where is it
> documented now that I own it ?
>
> Thank in advance,
>
> alabun
>
>
> _______________________________________________
> Linux-PowerEdge mailing list
> Linux-PowerEdge at dell.com
> http://lists.us.dell.com/mailman/listinfo/linux-poweredge
> Please read the FAQ at http://lists.us.dell.com/faq or search the list
archives at http://lists.us.dell.com/htdig/
>


--__--__--

Message: 3
From: Stig_Fjeldheim at Dell.com
To: alabun at spyderinc.com, linux-poweredge at Dell.com
Subject: RE: PERC 3/QC and memory usage ...
Date: Tue, 24 Jun 2003 02:42:17 -0500

Alan,

the support rep wasn't too far off.

The PERC3/QC board allocates 128MB worth of address space in the memory, and
based on the PCI architecture of the machine, it could multiply that a few
times. It has to map this to the upper end of the memory bus availiable at
boot-time, if I recall correctly, and that eats into the last parts of the
4GB. 

This is from the top of my head, so if you'd like a "confirmed" answer I
suggest you try contacting your support department again, and ask nicely if
they can escalate this to somebody who might get you the exact specs for
your combination of hardware.

Stig

-----Original Message-----
From: Alan Bunch [mailto:alabun at spyderinc.com]
Sent: den 24 juni 2003 06:28
To: linux-poweredge at dell.com
Subject: PERC 3/QC and memory usage ...


Dear assembled experts ...

PE 2650
4 g ram
PERC 3/QC controler
PERC 3/Di ROMB
Adaptec 39160

RHAS 2.1 @ version e25

Setup says I have 4096 mb of ram

I do not have OS setup mode turned on.

RHAS 2.1 says I have 3.5 g of ram

Memory diags says I have 3.5 g of ram.

Dell support says that each channel on the QC card take 128 mb of ram
explaining the .5 g shortfall in memory.

1. Did I just get the support rep who fell of the truck yesterday to
answer my call and this was the best guess he could come up with to
explain the facts ?

2. If this is in deed the case what does all of that ram get used for ?

3. How could I have known this *BEFORE* I ordered ? Where is it
documented now that I own it ?

Thank in advance,

alabun


_______________________________________________
Linux-PowerEdge mailing list
Linux-PowerEdge at dell.com
http://lists.us.dell.com/mailman/listinfo/linux-poweredge
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--__--__--

Message: 4
From: Mark Watts <m.watts at eris.qinetiq.com>
Organization: QinetiQ
To: linux-poweredge at dell.com
Subject: Re: PERC 3/QC and memory usage ...
Date: Tue, 24 Jun 2003 08:56:22 +0100

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1


> I'm going off what I know so here goes..
>
> #1 RHAS 2.1 says I have 3.5 g of ram
> The OS should be able to access all of it. This is part of a "highmem"
mode
> in the kernel. You can try passing it as a kernel option but you shouldn't
> need to. It should automatically do this, especially for a new OS such as
> RH AS. 32bit Kernels and programs only have access to 3.5GB of memory as
> the other 500mb of used for Kernel allocation and other 32bit functions.
> Any program (32bit only) including the kernel is only able to access upto
> 3.5GB. This is a limitation of the 32bit architecture. 64bit Architecture
> has higher adderesssing limts, upto 64GB (not 100% sure??) Again I'm not
> 100% sure, this is what I have learnt. Any single process (aka kernel) can
> only use 3.5GB at any one time. All programs started after the kenel (aka
> init) fall under init itself so they too can only get to 3.5GB of ram.
>
> #2 Memory diags says I have 3.5 g of ram.
> This would be because the Kernel suffers the same limitation. If the
kernel
> can only access 3.5GB then any program under will be the same. This would
> also apply for any Dell diags as they are 32bit programs, run via a DOS
> shell or shelldos command boot disk or "utiliity" mode partition. These
> also have the same memory addressing fallback as it's a 32bit program.
>
> #3 Dell support says that each channel on the QC card take 128 mb of ram
> explaining the .5 g shortfall in memory.
> The Dell PERC cards have additional memory chips on the motherboard. These
> are SDRAM chips @ 133mhz ECC.
> Your normal memory would be DDR @ 300+MHZ ECC (at a guess). So what Dell
> are telling does not sound correct.
> All PERC's I know of have their memory modules on the motherboard seperate
> from the system memory.
>
> Well the QC is a quad channel card? Correct? So if you were to boot the
> server with 4 x 128mb chips in your main DIMM slots you would essentially
> have no ram for the OS?
> What happens if you boot the server with 4 x 128mb ECC chips? Does this
> mean you boot with 0mb of ram? If what Dell is saying is true that means
> you would boot OS (RH AS) with 0mb of ram as Each of those 4 x 128mb chips
> would be used by the PERC QC. I'd be suprised if the PERC QC could use DDR
> instead of the traditional SDRAM @ 133mhz
>
> Interesting conversation...
>
> Anyone have any excact info?
>
> Hope this helps (dont take all my info 100% correct)

I'm prety sure that you _only_ loose 0.5G to the PCI bus(ses) if you have
4GB 
ram, regardless of what devices you have. The ram on the PERC cards has 
nothing to do with system ram - its purely a bigger cache than you get on
the 
drives themselves, and does exactly the same thing.

Mark.


- -- 
Mark Watts
Senior Systems Engineer
QinetiQ TIM
St Andrews Road, Malvern
GPG Public Key ID: 455420ED

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