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Oliver Salzburg
Asked: 2014-07-21 22:32:27 +0800 CST

Why are only 16 GB of memory usable on our server?

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We've recently upgraded the RAM on a Windows Storage Server 2008 R2 Standard to 32 GB.

When I open the System panel, it indicates Installed memory: 32.0 GB (16.0 GB usable). Why is that?

I've been trying to dig up documentation that would indicate that this is a limit of the operating system version, but I've come up short. Looking at the version comparison on Wikipedia shows no version with 16 GB, but Storage Server isn't listed and Memory Limits for Windows and Windows Server Releases doesn't list Storage Serer 2008 R2.

I've since found an infographic in the blog post titled Windows Storage Server 2008 R2 is now available!, which indicates that the limit would be 32 GB.

As suggested by @Nico, opening perfmon shows that 16 GB of memory are "reserved for hardware".

The board of the server is an Intel S3420GPLX set up with an Intel Xeon SP X3430, both of which are supposed to support 32 GB of memory.

The installed RAM modules are 4 x 8 GB Hynix HMT31GR7CFR8A-H9 RDIMM.

Support advised us to perform a firmware upgrade of the mainboard. We performed the firmware upgrade, but it had no effect on the issue

windows-server-2008-r2

6 Answers

  1. High end servers have options for pairing memory modules, like raid arrays for hard disks. You must view the BIOS option for that.

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  2. Have you see this link ?

    Running a Perfom /res would show you this "bug". Cause the missing RAM might be hardware reserved.

    Also, have a look at this Microsoft's KB : http://support.microsoft.com/kb/978610

    (I apologize, I cannot add any comment due to reputation)

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  3. It would be useful to know the exact configuration of RAM. i.e. the number of dimms, whether they're all udimm (unbuffered) or rdimm (registered). You can't mix udimms and rdimms on the board, and if you're using udimms you can only use 4/6 of the dimms and can only use up to 16GB of RAM - this sounds a likely cause for your issue.

    Reference - https://communities.intel.com/thread/21622

    It looks like, in order to get 32GB of RAM working on the board, you need a very specific configuration.

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  4. Many servers have separate RAM for each Processor, so if you have only 1 processor, then you either have to 1) install the 2nd processor or 2) install the RAM in the correct memory channel.

    (what hardware server do you have?)

    update:

    the manual says: 32 GB max with x8 ECC RDIMM (2 Gb DRAM) and 16 GB max with x8 ECC UDIMM (2 Gb DRAM)

    the model that you say youhave are RDIMM as far as I can see, but they do not seem to appear on the approved list of RAM modules here but not sure if that has any effect... looks like it is a BIOS or Windows thing then.

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  5. Best Answer

    In the BIOS, 2 of the modules were marked as "failed".

    Support advised us to test every module individually. The tech on-site tested different configurations, then put all the modules back in as they were and now the full 32 GB are usable.

    Not really sure what to make of it.

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  6. I agree with some of the answers listed already in particular with Mirrored Mode RAM.

    Also, according to the official Intel site, your particular memory is not supported for the board chipset.

    First thing I'd do is return the RAM back and get certified modules supported by the vendor.

    Then check if it requires the memory to be matched on each side of the banks i.e. two modules in the correct slots per side. There could be every chance the BIOS is also out of date.

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