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Re: Is this some kind of cluster?

From: Mark Bole <makbo_at_pacbell.net>
Date: Thu, 13 Jan 2005 20:44:17 GMT
Message-ID: <B4BFd.1499$8Z1.745@newssvr14.news.prodigy.com>


John wrote:
> I think it is not a cluster at all. I think there is just one UNIX box
> with 2 host name and 2 IPs assigned to it. Are there any reasons for
> doing this? I created a test file on one server. I immediately saw the
> same file on the other server.
>
> I've probably got a lot more to learn about UNIX (SUN Solaris, to be
> specific). The questions now then are
> 1. Why 2 IPs to a single host?
> 2. Why was I not able to connect when using one of the host name in the
> TNS alias?

[...]

> Well, Mark, I have no access to the hardware, hence all the head
> scratching. I lack complete DBA privileges, so I can not do a thorough
> database level check either. I thought it would be nice to be able to
> judge from all these information and figure out exactly what it is that
> I am dealing with.
>

[...]
>
> I am pretty sure it is just one box. Still I am not sure why there are
> 2 IPs and 2 hostnames assigned to it.

[...]

>>
>>Or like you suspect it is actually one machine with two different

>
> host
>
>>names and each virtual host (partition ?) having its own network

>
> card.
>
>>But I do not beleive you could access Oracle from both boxes at one
>>time without RAC to coordinate the block updates.
>>
>>If you shut Oracle down on one side does it disappear from the other.
>>If so then it would appear that it is really just one and the same
>>database.
>>

[...]
>>
>>-- Mark D Powell --

>
>

Since you are starting with not much understanding, here's to clarify the use of "hostname". A hostname is just a name applied to a computer for convenience. Even a computer with no networking capability at all can and should have a hostname.

A machine can have one or more NICs (usually ethernet) and one or more IP addresses for each NIC, usually on different subnets per NIC. This is not unusual for servers even in small organizations to help segment LAN traffic, for example application data one subnet and administrative logins on another. Such a machine is called a multi-homed host, and each network address will typically have a unique name, which is independent of the hostname (although people commonly refer to machines   by one of the names of one of its network addresses, since that is how they normally access it, rather than by the hostname).

So, if you log in to each of what you think might be two physical machines and see the exact same information when you run the "ifconfig -a" command on each one (including the ethernet addr), then it is almost certain that it is actually one and the same machine. The output of the "hostname" and "hostid" commands can help corroborate this as well.

The Oracle listener(s) can be configured to use all, none, or some of the available IP addresses on any given machine, so that most likely explains why your TNS experiment failed.

I share hpuxrac's curiousity how this forum could be considered the best first place to come for information on such a site-specific question--why don't you ask the owner of the machine(s), or whoever granted you access? This is even more basic than RTFM...

-- 
Mark Bole
http://www.bincomputing.com
Received on Thu Jan 13 2005 - 14:44:17 CST

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