RAM question for HP Z800 Workstation

[Rich999999]

Hi, I have acquired an old Z800 workstation. It's a single CPU, with 6x2Gb ECC Registered RAM. I'm planning on getting rid of that, and putting in either 8 or 16Gb sticks. From reading the specs, 8Gb is straightforward - just get some DDR3-1333 ECC. However I had a question about 16Gb sticks - the specs state that it supports 16Gb quad-rank, but that they will run at 1067MHz, not 1333MHz. I'm assuming this was written when you could only get quad rank 16Gb DIMMs. I can now find single, double and quad rank 16Gb ECC DDR3 DIMMs for sale - am I right in thinking that if I got single or double rank 16Gb DIMMS, they would work, and would operate at 1333MHz? Or do I have to buy quad rank, and assume they will drop down to 1067MHz?

Thanks!

[DGroves]

so far as i know, only quad rank 16gb registered dims exist

check carefully as sellers may advertise 2 8gb modules as 16gb "total"

[SDH]

You want to know if you have a version 1 or a version 2 Z800.  You can tell from BIOS, from the boot block date.  The memory controllers changed....

[Rich999999]

Thanks - based on the boot block, it's v2. 

Regarding ranking, I can find 16Gb registered DDR3 modules that claim to be single/dual ranked. E.g. these say they are dual:

https://www.scan.co.uk/products/16gb-crucial-ddr3-pc3-12800-(1600)-240-pins-ecc-registered-cas-11

Based on the fact I have v2, what 'Ranks' of 16Gb RAM should I be buying for compatability and/or speed?

[DGroves]

i would stick with quad rank modules, as that's what HP tested/designed the system for using dual rank modules may actually be slower

i recommend you read up on what a memory "rank" actually is  if you google it you will find numerous references to it some are quite advanced or hard to understand but here's a brief description

t is important to ensure that DIMMs with appropriate number of ranks are populated in each channel for optimal performance. Whenever possible, it is recommended to use dual-rank DIMMs in the system. Dual-rank DIMMs offer better interleaving and hence better performance than single-rank DIMMs.

For instance, a system populated with six 2GB dual-rank DIMMs outperforms a system populated with six 2GB single-rank DIMMs by 7% for SPECjbb2005. Dual-rank DIMMs are also better than quad-rank DIMMs because quad-rank DIMMs will cause the memory speed to be down-clocked.

Another important guideline is to populate equivalent ranks per channel. For instance, mixing one single-rank DIMM and one dual-rank DIMM in a channel should be avoided.

---

Ultimately, the effect of the number of memory ranks is specific per server/chipset. For example, on IBM's x3850X5 servers more ranks is better (see §3.8.4):

With the Xeon 7500/6500 processors in the x3850 X5, having more ranks gives better performance. The reason is because of the addressing scheme, which can extend the pages across ranks thereby making the pages effectively larger and therefore more page-hit cycles.

[Rich999999]

Thanks for the advice - I did google a bit, but a lot of it went over my head. I was just operating on the principle that quad ranks lead to downclocking of the memory bus, which is undesirable!

[DGroves]

as i said hp specs quad rank, but as those were the only commonly available dims at the time it is possible that a dual rank might be faster and possibly prevent a bus speed down clock

so if you can do a return on the memory, try the dual rank and note the bus speed, if it runs at the faster speed then i would think that will give faster performance overall

[DatabaseOfuser]

Come on! Drop that playing. You got an ol'timer. Don't mind speeds, get a second cpu and use 3-chanels on both of them. RAM speed WILL double!

[SDH]

Speaking of playing.....'

There are several reasons HP does not list something as approved.  An obvious one is that the engineering team tried and it did not work.  Another more subtle reason is that they never tried and thus could not certify it to work.  In that case it might be due to the item being unreasonably expensive to have a market at the time.  Some items that were ungodly expensive for one market might have had another market in which that cost was justifiable.  For example, big memory in an enterprise server.  A workstation that is server-like in its engineering would not have a large enough market for that very expensive memory to justify the extensive HP certification process costs, yet that memory might work well in the right HP workstation.

Then, time passes and things change.  Enterprises buy the next generation faster better HP servers and surplus this item..... memory sticks.  The market may glut as a result, and they become available at a price now reasonable.  In some cases we here do the testing HP bypassed years earlier and find out the item works just fine and is now affordable.  Don't expect HP to go back to End Of Life HP workstations and do another round of certification.....

I've mentioned borrowing 8GB sticks of HP ECC PC3-14900R running in one of our Z620 version 2 workstations and running 6 of those sticks in one of our version 2 Z600 workstations.  That faster 1866 MHz rated memory automatically down-regulates to the fastest the Z600 version 2 workstation can run (1333 MHz) assuming the Z600 has a fast enough processor.  I'm on the hunt right now to test the same concept with 16GB sticks..... and will get back to you if I pull that off.   I want to use only HP sticks so price is an issue because I really don't need to run a Z600 with 96GB of memory.  I get to test in both the Z620 v2 and the Z600 v2.  I tend to use the Samsung HP memory for these projects.

Read up on whether your Z800 is a version 1 or a version 2... get the boot block date from BIOS.  This method would be expected to potentially work only on a Z600 or a Z800 if they are version 2 workstations, and will never work on a Z400 regardless of v1 vs v2 status. 

[SDH]

Ordered the 1866 HP 16GB sticks.... quite sure they will work on a souped up Z620 version 2 here.  The more interesting question is whether these ECC buffered HP sticks will work on a Z600 version 2, down-regulated to the appropriate lower speed.  There will be no loss.... we can use these in the Z620 version 2 if they don't work in the Z600 version 2.

Sometimes we need to test for ourselves.  I just ordered 6 sticks.  I really don't like to order less than HP sticks because of the odd issues I have seen otherwise in the past.