two identical machines - substantially different hash - Why?

[Viceroy]

What could cause two identical machines to display substantially different hash rates?

1) cgminer/Drivers/OS/Hardware are Identical
2) Temperatures are fine, and lower on the slower machine.
3) Machines are not overclocked or under-clocked
4) The machine with only two cards is running slower


Working:

Code:

--------------------------------------------------------------------------------
 [P]ool management [G]PU management [S]ettings [D]isplay options [Q]uit
 GPU  0:                | 257.6M/210.0Mh/s | A:4 R:0 HW:0 U: 1.94/m I: 9
 GPU  1:                | 241.3M/209.1Mh/s | A:7 R:0 HW:0 U: 3.40/m I: 9
 GPU  2:                | 245.5M/211.0Mh/s | A:5 R:0 HW:0 U: 2.43/m I: 9
 GPU  3:                | 238.9M/209.7Mh/s | A:4 R:1 HW:0 U: 1.94/m I: 9

Broken:

Code:

--------------------------------------------------------------------------------
 [P]ool management [G]PU management [S]ettings [D]isplay options [Q]uit
 GPU 0:                | 26.30M/42.08Mh/s | A:1 R:0 HW:0 U: 0.70/m I: 9
 GPU 1:                | 26.28M/42.67Mh/s | A:0 R:0 HW:0 U: 0.00/m I: 9
 GPU 2:                | 26.08M/42.47Mh/s | A:1 R:0 HW:0 U: 0.70/m I: 9
 GPU 3:                | 26.05M/38.76Mh/s | A:0 R:0 HW:0 U: 0.00/m I: 9

[1715020957]

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[Zeronic]

Have you tried swapping the cards between the machines, might have a bad MB.

[Viceroy]

Have you tried swapping the cards between the machines, might have a bad MB.

You may be right, or a badly seated card....

Code:

two GPU's, Card A

--------------------------------------------------------------------------------
 [P]ool management [G]PU management [S]ettings [D]isplay options [Q]uit
 GPU 0:                | 283.5M/300.8Mh/s | A:2 R:0 HW:0 U: 3.40/m I: 5
 GPU 1:                | 283.7M/300.7Mh/s | A:1 R:0 HW:0 U: 1.70/m I: 5
 GPU 2:                | OFF   / 0.000h/s | A:0 R:0 HW:0 U: 0.00/m I: 5
 GPU 3:                | OFF   / 0.000h/s | A:0 R:0 HW:0 U: 0.00/m I: 5
--------------------------------------------------------------------------------

two GPU's, Card B

--------------------------------------------------------------------------------
 [P]ool management [G]PU management [S]ettings [D]isplay options [Q]uit
 GPU 0:                | OFF   /2.487Mh/s | A:0 R:0 HW:0 U:0.00/m I: 5
 GPU 1:                | OFF   / 0.000h/s | A:0 R:0 HW:0 U:0.00/m I: 5
 GPU 2:                | 95.80M/34.02Mh/s | A:0 R:0 HW:0 U:0.00/m I: 5
 GPU 3:                | 86.04M/31.47Mh/s | A:0 R:0 HW:0 U:0.00/m I: 5
--------------------------------------------------------------------------------

[c789]

I had this happen on Xubuntu with 2 cards. What worked for me was using a dummy plug. I only needed 1 dummy plug to make both of the cards get their full hash rate.

If you don't have a dummy plug handy, try this:

Stop cgminer
Plug in a monitor
Start cgminer

Try that with each of the DVI outputs. For me, having the monitor (or dummy plug) in card 0 in the top slot worked.