HOWTONOT: upgrade memory

[vermaden]

I add this little 'story' here as a warning, that may be helpful for performance troubleshooting.

Some time ago I bought used MINI ITX motherboard with Intel T8100 CPU and 965GM chipset, it came along with used 2 x 512MB RAM 667MHz DDR2. I already had 2 x 2GB RAM 800Mhz DDR2 from my older box, so the first thing I did after assembling all the parts was upgrade the amount of RAM.

The system worked well, 50+ days of uptime until power loss from time to time, it has ZFS mirror on 2 x 2TB drives. But I 'found' some strange performance problems.

So I started to look for the cause of the problem.

First I thought its slow because I have 80% filled ZFS, but after upgrade to 8.2-STABLE and various performance improvements it should not be a problem.

Then I thought that CPU may be overheating ... but it wasnt.

My 2TB disks are LOW POWER Seagate's so I thought that maybe their random access time is so low that its because of that, nope.

I also thought that it may be because of maybe broken 8GB CompactFlash card that is used for hte base system, nope.

At that point I did not had any clues what to check more.

But I thought, maybe I will also check memory ...

I found some nice simple memory allocation benchmark called ebizzy (nor in ports) and run # ebizzy -s 4096 to check the speed, compared with memory allocation speed on somparable laptop ... and VIOLA! Thats the problem.

I have just 'degraded' memory from 4GB 800MHz to 1GB 667Mhz and now allocations in ebizzy raised from 11462 records/s into whooping 2347823 recors/s

Also ffmpeg performance improved from 0.2 FPS into ... 40 FPS

Its because 965GM chipset maximum frequency is 667 MHz.

You have been warned ]:->

[Oko]

The story sounds little bit strange since DDR 2 800 is suppose to be backward compatible with DDR 2 667. In another words. DDR 2 800 should have been detected as 667 if that is what the maximum memory speed of your mother board should have been.

Oko

[vermaden]

That's what I also thought, I checked BIOS options, but this motherboard does not offer any manual settings for the memory.

[Carpetsmoker]

You may have a case of broken memory. If in doubt, run memtest for at least a few hours.
Memtest also reports the memory speed by the way...

What mainboard do you have by the way?

[vermaden]

Originally Posted by Carpetsmoker

You may have a case of broken memory. If in doubt, run memtest for at least a few hours.
Memtest also reports the memory speed by the way...

I have used that memory in my previous box for more then a year with 100+ days of uptime and as I said I did not had any stability problems either here, everything was just painfully slow.

Originally Posted by Carpetsmoker

What mainboard do you have by the way?

This one mate: http://us.msi.com/index.php?func=pro...8&prod_no=1187

[Carpetsmoker]

That is worked last week says exactly nothing on the current state of your memory

It's true that this chipset doesn't support 800MHz memory, but in general it should work fine. I've often used 800MHz memory with this chipset and never had a problem. It will just run at 667MHz

I would say either your memory is broken, there is some BIOS option to manually switch this, or there is a problem with the mainboard and/or BIOS.

[vermaden]

@Carpetsmoker

Here is some input from OH about that issue, it can be the 'uncacheable bug' in the Intel 965 chipset when using 4GB or more memory:
http://forums.freebsd.org/showthread.php?t=23684

[rpindy]

Yeah, that is odd. I added two 800 MHz sticks to a computer with two 533 MHz sticks already in it and it worked fine. The BIOS recognized it as 800, so I think they just didn't put the max MHz RAM in to begin with.