SUMMARY: E450 question on DIMM

Robert.Barkhymer at rcn.net Robert.Barkhymer at rcn.net
Fri Nov 9 11:44:56 EST 2001


Thanks to all that responded.John pretty much sums it up.

QUESTION:
    I have read recently that on the SUN E450 Server performance can be
>enhanced if bank A and bank B are filled with the same size DIMMs so that
>memory interleaving becomes possible between the two banks. And can be
>further enhanced by filling all four banks with the same size DIMMs which
>will allow 4 way memory interleaving between all banks. How much of a
>difference in performance will it have??? We currently have two E250's
with
>the following Memory and before I make any changes I would like to know if
>it will make a significant difference? For example I have 4x128Mb and if I
>replace the B bank which is currently 4x256Mb will it improve it? It will
>be less memory but A&B will be equal.
>
>
>CPU  4 X 400 MHz
>Mem  3584Mb     Total
>Type  E450
>
>     Bank     (MB)
>     ----           -----
>     (A)0x4    128
>     (B)1x4    256
>     (C)2x4    256
>     (D)3x4    256



ANSWER: (from John M. at Star systems)
The answer is clearly that you will gain some performance. Sun's best
number,
put forth so far, is a gain of about 5-10%.

I've also read that it depends on the type of applications and how these
apps
use the memory to begin with.

Here is about the best answer I've receive from someone who has actually
done
performance measurements. Keep in mind that this was done on an Enterprise
class
machine with multiple system boards, which helps the performance of memory
interleaving even more.

EXX00 class server memory interleaving performance tests:

bd1 1GB mem bandwidth 500MB/s
bd2 1GB mem bandwidth 500MB/s
bd3 1GB mem bandwidth 500MB/s
     total mem bandwidth 1500MB/s

bd1 1GB  1GB  mem bandwidth 600MB/s
bd2 1GB           mem bandwidth 300MB/s
bd3 1GB           mem bandwidth 300MB/s
     total           mem bandwidth 1200MB/s


As you can see, and the only piece that really relates to you with a single

system board in your E450 is the second section. It shows that the system
board
with 2 banks of 1GB of memory gives you the added benefit of 600MB/s
instead of
500MB/s. That is a 16.7% improvement which is more than the 5-10% Sun says.

Remember that the 16.7% is raw bandwidth and when are you ever going to get
true
use of the full bandwidth? Probably never.


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