Server Performance when memory isn't matched

networkn
networkn used Ask the Experts™
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Hi There!

We have deployed a HP Proliant ML350G6 with 12GB for SBS 2011. It doesn't seem to be enough and the only cost effective upgrade for this client is another 6GB to a total of 18GB.

The current config is 6x2GB which is running at full speed, but as I understand it, if I populate the 3rd banks then the server memory performance will drop. It's a single processor server.

How much real world performance will the end user notice if we use this non performing memory configuration?
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VP Technical Sales
Commented:
short answer: no performances decrease will be noted !

long answer : no performances decrease will be noted, but you should take a look to the following document to buy the right type of memory for the right cpu on the right bank:

http://h18000.www1.hp.com/products/quickspecs/13241_div/13241_div.html#Memory

In particular:
Do not install DIMMs if the corresponding processor is not installed
If only one processor is installed in a 2CPU system, only half of the DIMM slots are available

Lot's of differences are based on the rank level of your current dimm

Check the configuration examples on the document


Author

Commented:
Hi There!

I was intending to use the identical memory to the existing memory. 6x2GB and I was going to add another 3 x 2GB of the exact same time. Is this ok?
Frank ContrepoisVP Technical Sales

Commented:
Yes :-)

based on the document original memory is  2GB RDIMMs so no problem
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Top Expert 2014
Commented:
The slowdown of the memory bus won't be noticed because it is still going to be far faster than the next best thing which is getting the data off the disk.

You'd be better off getting a 4GB and a 2GB than 3*2GB though, cheaper and no noticeable performance difference - then you'd put 4+2 on channel 1, 2+2+2 on channel 2, and 2+2+2 on channel 3. That would still have 6GB on each channel even though bank 3 would still be populated so slowing the bus down to 800MHz.

Do you have any use for 3*2GB , for example for another customer? Then you could take 3*2GB out and replace with 3*4GB and keep the faster bus speed rather than drop down to 800MHz.
Top Expert 2014

Commented:
OH, BTW, there's another upgrade you might need that isn't RAM related, base models of ML350G6 don't have the battery required to enable the write cache on the disk controller, fitting that can seriously improve disks write speed, especially if you have RAID 5.

Author

Commented:
This customer bought a model with 512MB Cache and is running RAID5 :)

Author

Commented:
this is off original topic, but in a 15 user site, with 12GB, should we be seeing 98% physical memory use?
Top Expert 2011

Commented:
Please note that exchange 2010 and sql 2008 R2 (both included with SBS 2011) are designed to allocate almost all memory. This is no problem, it is by design, if other application need the memory it will release memory if possible. So adding extra memory won't change the memory usage looks, in that case you could continue adding memory, so this is only needed if you have serious performance issues.
Top Expert 2014

Commented:
Not sure if it's SBS without SQL, but for example SQL takes as much RAM as there is available and releases it only if another application needs it so utilization close to 100% is expected. I think Exchange 2011 also grabs what RAM it can, hopefully an SBS expert can confirm this.
Top Expert 2014

Commented:
Thanks for confirming Ronny, I forgot to refresh screen :)

Commented:
To improve performance, I suggest adding a 2nd CPU and evenly distribute your memory modules!
Top Expert 2014

Commented:
I wouldn't, better to spend $300 on more RAM than on a second CPU normally. Having more RAM is generally more important than having a perfectly symetrical  configuration.
Top Expert 2011

Commented:
I wouldn't suggest an extra processor either, for 15 users a single processor with 12GB ram would be fine, if you have some performance issues upgrade the ram to 18GB will be good enough

Commented:
Adding an extra CPU would be future proof.. and add extra kick to your system then add more RAM. This will also allow you to add more RAM if required. I'm just thinking from a present and future point if view so you don't need to upgrade for along time but adding more RAM down the track.

Author

Commented:
Thanks for the help everyone.

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