[Linux-HA] heartbeat with only 1 NIC per server?

[Rudi Ahlers]

Max Hofer wrote:
> HA is about redundancy. This means having 1 NIC will
> probably not make you system very reliable.
>
> Does the NIC have 2 ports?
>
> Your worst case scenario (as I can think of):
> - connection failures to one of the NICs (!not NIC failure)
> which will turn off/on/off connectivity (this may be cabling
> problems, switch problems etc.)
> ---> your cluster will split, rejoin, split rejoin. And I'm sure
> it will not take long and you have a split brain problem.
>
> Back to your question:
> - we run heartbeat over the LAN, not a big problem if you use 
> it only to share heartbeat data (i.e. no big data is transferred 
> like DRBD devices etc.).
>
> Your problem is that you do not have connection redudancy 
> between the cluster nodes.
>
> Possible solution: what about interconnecting the two servers
> with a serial cable? At least you will avoid the split brain problem
> when the network fails.
>
> WHat about USB connections?
>
> kind regards Max
>
> On Monday 23 July 2007, Rudi Ahlers wrote:
>   
>> Hi all
>>
>> I hope someone can assist me with this one. I previously (almost a year 
>> ago) setup heartbeat on 2x Suse 9.3 machines, where each server had a 
>> wireless NIC & a onboard NIC. The network ran on the wireless NIC's, and 
>> I then used the onboard NIC's with a crossover cable to monitor heartbeat.
>>
>> Recently, we took out the wireless network, and put in a 8 port 10/100 
>> switch to run eveything on. So, each server now only has 1 NIC. The 
>> wireless gave us too many problems, and getting working cards was a 
>> problem. To put it differently, the client is 700KM away, and not IT 
>> literate, so we had to fedex the wireless NIC to them, and try and make 
>> it work over the phone. Bottomline, running a normal CAT5 LAN is less 
>> error prone.
>>
>> So, to get back to the question. How stable / safe / redundant is it to 
>> run heartbeat over the same NIC's as the LAN?
>> If server 1 use IP 192.168.0.5, server 2 use 192.168.0.6 & tell 
>> heartbeat to server 192.168.0.3 on the LAN, will this work well enough?
>>
>>     
The onboard NIC's are standard one-port NIC's, and from there the 
servers connect directly into the 8 port 10/100 switch.

I hear what you're saying, and it makes sense.

But, here's my situation. The whole network runs on 1 switch (only 7 
PC's), so if the switch were to fail, so does the network. If the Mobo / 
CPU / PSU / RAM were to fail on on the (standard PIV) servers fail, the 
server fails. Thus, in either case a second NIC won't help me much. The 
only reason I use heartbeat, is to make sure there is at least one 
server up, serving the IP address 192.168.0.3. I use MySQL replication 
to replicate the MySQL DB, rsync to replicate the intranet, and 
different DHCP ranges to make sure every PC can get a DHCP address.

So, there's no critical data going across the LAN for heartbeat.

What is the USB stuff that you're talking about?

Kind Regards
Rudi Ahlers
CEO, SoftDux

Web:   http://www.SoftDux.com
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