Inline self-terminating cable requirements

[Vincent Farrugia]

Hello,

We have a customer whose system consists of a 3-node cluster and 2 SC10s. If one node fails, the system migrates to the middle (spare) server. It is shown in the diagram attached.

We need to know what cables need to be self-terminating and which one doesn't. The customer is telling us that the 4 cables connecting the middle and the bottom servers only need inline termination. We think all 6 cables need inline termination. What do you think?

Vince

[Christopher Caldwell]

If you're doing maintenance, anywhere you expect to be able to remove a card from a multi-connected device (host side or storage side) w/o affecting the other equipment hooked to that device (i.e. you don't want to turn off the equipment) needs an in-line terminated cable.

e.g. if you've got two boxen hooked to an array via common bus, different controllers; A is main; you failover to B; and you want to replace the SCSI card on A; you've got to have an in-line terminated cable, or you have to take an outage.

[Sanjay_6]

Hi Vincent,

I think your suggestion is a good one. As per the layout you have given, you should use 6 cables with inline terminators. It is advisable to put the inline terminator cables on the server side.

Here is a thread which might help you,

http://us-support.external.hp.com/cki/bin/doc.pl/sid=2f47315206a053947f/screen=ckiDisplayDocument?docId=200000009872407

Hope this helps.

Regds

[Vincent Farrugia]

Hello,

Thanks for your replies, I will assign points later.

I just wanted to double-check (or triple-check anyway)... any other guys voting for 6 cables as opposed to 4 cables? :-)

Vince

[Sanjay_6]

Hi vincent,

You may want to modify your configuration in this manner. Here you have to use, 4 V-cables on the SC10 side,

server1 --> L1
server2 --> L2
server3 --> L3
SC10-1 --> S1
SC10-2 --> S2
SCSI Channel-1 --> C1
SCSI Channel-2 --> C2

The cabling should be like this,

L1(C1) -->S1(C1) -->L2(C1) -->S2(C1) -->L3(C1)

L1(C2) -->S1(C2) -->L2(C2) -->S2(C2) -->L3(C2)

Here both the SC10 sit in between the servers and are using two channel from each server. Gives you good redundancy.

Hope this helps.

Regds

[Vincent Farrugia]

Hello,

I didn't understand how to connect the V-cables. V-cables connect to 3 nodes as far as I know. How could you connect 5 nodes with V-cables? Is there a "W-cable" for this? :-) My concern is on L2(C1) and L2(C2)... how do you connect the V-cables there?

Also, the SC10 has an other BCC, you didn't mention this second BCC. Or else I assume you use both BCCs and you put a terminator on the other free ports?

Vince

[A. Clay Stephenson · Accepted solution]

Actually, I agree with your customer. If I can follow your diagram, your top server is a direct connect to both arrays. If you have to replace a card in the top server you're going to have to down the box anyway - you could use in-line termination but it just doesn't buy you much. Your other connections are multi-hosted so in-line termination is required. I might be more tempted to use a V-cable to connect all three 3 servers on the same bus with in-line terminators on the ends of the bus. You seem to be confused by the construction of a V-cable. Really it's closest analogy is an old BNC Tee as used in 10-Base-T (Thinet). Moreover, just like the BNC Tee's no 'pigtails' are allowed. You must attach the 'V' section directly to the host bus adapter without any short piece of cable. You then simply plug traditional scsi cables into the ends of the 'V'. Again, think of it as a 'T' - cable.

Regards, Clay

[Vincent Farrugia]

Hello,

Awesome answers, yet again. Very helpful... Thanks Sanjay for the suggested cabling diagram, and thanks Mr. Stephenson for explanation!

Case closed.