[Beowulf] Opteron nodes w/PCI-E (for 4x IB)

[Mikhail Kuzminsky]

I'm looking for possible choice of chipset (and therefore
motherboards) for dual Opteron-based 4U-nodes (i.e. higher than 1U :-)
!) having PCI-E (PCI-Express) support. 

I need PCI-E x8 for Mellanox MHGS18 or MHGA28 HCAs 
having DDR mode (20 Gb/s). So the only choice, IMHO, is:

1) ServerWorks BCM5780/5785
- for example, Tyan Thunder K8HR (S3891) having
PCI-E x16 w/2 * x8 signals

2) AMD8000 + nVidia nForce4 Professional 2200
- for example, Tyan Thunder K8SE (S2892, or may be
K8SRE=S2891) having PCI-E x16.
As I understand, any x16 slot is appropriate for x8 cards
(is it right ?)

I prefer Tyan mobos simple because I have good experience w/Tyan
(Supermicro products were usually more expensive).
But what is known about pluses or minuses of this chipsets
(or motherboards) - especially in the sense of reliability etc ?

ServerWorks looks for me as more solid; nVidia chips required 
(in the past) some needs to install own Linux drivers etc.       
But ServerWorks-based Tyan S3891 is absent currently in Russia,
and S3892 costs about $750 (something about USD 200 higher
than S2892), so nVidia Prof 2200 is preferred for me today.

BTW, more cheap dual Opteron motherboard w/PCI-E support is
Supermicro H8DCE-B (again nVidia; formally
for workstations; but I may try to find 2nd hand PCI-32 graphics
card for it :-))

Thanks for your help in the future !

Mikhail Kuzminsky
Zelinsky Institute of Organic Chemistry
Moscow