[CentOS] Question about clustering

Mon Jun 16 17:55:21 UTC 2014
Digimer <lists at alteeve.ca>

On 16/06/14 01:36 PM, John R Pierce wrote:
> On 6/16/2014 2:39 AM, Alessandro Baggi wrote:
>> Hi Digimer,
>> there is a chance to make fencing without hardware, but only software?
> the most common fence in TCP connected systems is to disable the
> ethernet ports of the fenced system, done via a 'smart ethernet
> switch'.   if you're using shared fiber storage, then you fence via the
> fiber switch.  a more extreme fence is to switch off the power to the
> fenced system via a 'smart PDU'.

Disconnecting a lost node from the network is a process called "Fabric 
Fencing". It is not the most common, at least not these days. In the 
past, fencing was done primarily at the fabric switch to disconnect the 
node from shared storage, however this isn't as common anymore. These 
days, as you say, you can do something similar by turning down managed 
switch ports.

The main downside to fabric fencing is that the failed node will have no 
chance of recovering without human intervention. Further, it places the 
onus on the admin to not simply unfence the node without first doing 
proper cleanup/recovery. For these reasons, I always recommend power 
fencing (IPMI, PDUs, etc).


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