Memory Requirements on N4000-100-440

[Gerhard Roets]

What is the maximum reccomended memory to be used on this chassis, for optimal performance. Please keep in mind the peak memory bandwidth requirements with the Memory Carrier Boards.

Will there be any paging issues.

Thanks for your trouble in advance.

Gerhard Roets

[paul courry]

As always it is always a good idea to stuff a box as full of memory as you can afford.

Make the first bank HP and the rest a good quality 3rd party memory (support contract issues).

The issue is not peak memory bandwidth or anything else, but trying to keep the box from going out to those slow, slow disc drives. The fewer times the box has to swap out pages or go out to the disks for more data the faster the whole shebang runs. The way the hardware manages fetches from disk now a days (it gets great big chunks of data) you get your best performance from machines with lots and lots of memory.

[Eric Sorensen_1]

Hello Gerhard,

I searched, but I could not find any indication of a problem with "too much" memory. The standard recommendation is just as Paul said: install as much memory as you can, because it reduces the time the CPU waits for the data to be made available to it. After power-patch 70.01, the N-class supports 16 GB. The Very Low Latency Memory Controller sits on a Merced bus that can transfer many gigabytes per second. The system is capable of supporting 8 PA-8600 CPUs. I really doubt there is a potential for a memory bottleneck.

[Gerhard Roets]

Let me extrapolate a bit ...

There was a issue with a k-series(1 way) e3000, where with to much memory(+- 8GB) it would get intermittand slowdowns as the machine is writing memory blocks to disc. Just want to make sure this won't happen again. A previous patch might have fixed it im not sure.

My thought, is going from 384MB to 2GB is a large enough jump compared to a jump to 8GB.

If there is no such issues as mentioned above, is the jump to 8GB really worth the cost?

Thanks for your input thus far.

Gerhard Roets

[Mark Landin]

The old rule has always been "as much memory as you can afford". Unfortunately, accountants prefer the rule "as much as you can JUSTIFY".

You asked if you really need 8GB. Well, nobody can answer this question better than YOU. You might want to start with some reasonable inital memory amount ... maybe 2GB. Then run your application and use a tool like Glance or SOS/3000 to monitor the performance of your system. If you see a large I/O wait rate, or high paging activity, then you probably need more memory. If, on the other hand, your application is CPU-bound or network bound, then more memory probably isn't going to help.

You don't ALWAYS need more memory when there is a performance problem. Know WHY your application is bottlenecked before you throw money at removing the bottleneck.

[paul courry · Accepted solution]

Gerhard,

That K-class issue had to do with a user settable parameter that HP has since done away with. It allowed the user to control when the transaction buffer got flushed to disc. This "feature" caused so much trouble that HP yanked it out.