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

[Rudi Ahlers]

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?