[Info-vax] satellite with more than one boot server

[Stephen Hoffman]

On 2013-02-02 14:28:49 +0000, Phillip Helbig---undress to reply said:

> In article <Bk3XXRgOnZgg at eisner.encompasserve.org>,
> koehler at eisner.nospam.encompasserve.org (Bob Koehler) writes:
> 
>> Any MOP server that is serving MOP in the cluster can download the
>> image.  Any disk server that is serving the system disk can
>> complete the boot service.
>>> 
>>> Is there any reason not to configure a satellite to boot from more than
>>> one boot server in a given cluster?
>> 
>> Having more than one provides redundancy, you can set up the
>> satellite so that it can run while either server is down.
> 
> So the satellite requests a MOP download and essentially any machine can
> serve this request.  OK.

This is listed in the clustering manuals as boot servers and disk 
servers.  They don't have to be the same.

> Then the satellite requests a boot and any
> node which is configured can boot it.  Except for the ethernet address
> of the satellite, which of course is fixed, these configurations could
> presumably be identical or completely different (SCSSYSTEMID, IP
> address, ALLOCLASS, SYS$SPECIFIC).

Yes.  The fastest boot server wins.  The other boot servers usually get 
a "line open" error logged, indicating there was a collision detected 
on the network.

The downside is a disk or boot server that doesn't have local (fast) 
access to the boot disk.  That overhead can clog even a gigabit 
network, particularly if you've also got HBVS in play and start 
slinging piles of blocks around for that.

> I'm not sure if I would prefer them
> to be identical or different.  If I opt for different, the only
> potential problem would be with TCPIP, and then only if I have common
> TCPIP configuration files (i.e. for all system disks in the cluster).

It's extremely rare to have different boot configurations served in 
parallel, by default.

There's usually one default mapping to one default boot root with one 
default version, etc.  That might be served from one boot server, or 
from multiple boot servers.

There's also variously an InfoServer configuration which can be 
explicitly booted, which can be a handy way to keep "template" systems 
around.

> IIRC, some node-specific TCPIP stuff is not in SYS$SPECIFIC but rather
> in SYS$COMMON (or, when properly set up, somewhere else, even off the
> system disk) with the node name used as a key.  Is this right?  If so,
> then at least the TCPIP configuration would have to be the same.

DECnet and IP tend to have the most examples of this.  But nothing 
prevents you from having a dozen identical SYS$SPECIFIC configurations, 
or a dozen different, either.  Where you're potentially headed — 
different boxes booted from the same root — is painful however, not the 
least because the available devices and the device names tend to differ 
among different boxes.




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