[Linux-HA] Questions re: USB for HB and n-node data storage

[Madison Kelly]

Rudi Ahlers wrote:
> 
> 
> Madison Kelly wrote:
>> Morning all,
>>
>>   I've been mulling over how to move to an n-node cluster... I've got 
>> my two-node cluster working nicely, so this isn't critical. I just 
>> want to learn. :)
>>
>>   I've not found any good docs on how to do n-node, so I've been 
>> trying to think of it myself (scary!). One limitation I saw was the 
>> backup serial link for HB. I was thinking that I would need n-1 serial 
>> ports per server to let all nodes talk to all other nodes, but this 
>> seemed problematic as I use 1U servers and I'd need to waste a 
>> (precious) expansion bay for a multi-port serial card (if this was 
>> even possible!).
>>
>>   So I was wondering, is it possible to use USB for HB? I think I saw 
>> it mentioned that it was possible, but have seen no docs for this. If 
>> it is, how possible/reliable would it be to have a USB hub for n-nodes 
>> so that I'd only need one USB cable going into each server?
>>
>>   Secondly,
>>
>>   As I understand it, DRBD only supports two nodes. I know OCFS2 
>> supports n-nodes as an FS, but no help if the underlying block device 
>> doesn't. How do people get around this limitation? I am hoping to 
>> avoid the need for fancy hardware, as we are a very small company. 
>> Would OCFS2 formatted NAS device work?
>>
>>   Thanks for any pointers!
>>
>> Madison
>>
> This sounds like a great idea.
> 
> I have one important question though, what type of USB cable does one 
> use for this type of operation? And how do you overcome the problem if 2 
> of the 4 node cluster is in another room (say on the second floor of the 
> building), or something like that?

For the USB, I would *suspect* you would use a data transfer style cable 
(cross over equiv.?)... But I am not sure, hence my question this 
morning. :)

As for long throw, I haven't even begun thinking of this as I am still 
working on the basics. For serial, I would probably use those DB9-RJ45 
adapters and run a long CAT5(e) cable. Not sure if there is something 
equivalent for USB. In my case, I would have the nodes in the same rack 
for now. It's certainly an interesting question, and one I plan to look 
at down the road as I learn more.

Madi