[c-nsp] ISSU on SXF -> SXI

[Rob Shakir]

On 12 Feb 2010, at 12:29, Phil Mayers wrote:

> * The old and new image are not ISSU-compatible (different major releases or feature sets) - in which case an RPR upgrade is the best you can do.
> 
> * The old and new images are ISSU compatible, and the linecard software has not changed. In this case, the linecards do not need to be restarted, and downtimes of 0-3 seconds can be achieved because it's basically just an SSO switchover.
> 
> * The old and new images are ISSU compatible but the linecard software is different, so the linecards need to be restarted into the new image - this can be a faster, warm boot (if the linecard has enough RAM) or a slower, cold boot (if not)
> 
> I think that's about right?

This seems quite accurate to me.

Our experience of ISSU has been terrible. We've found multiple bugs related to it, and have found that -- in general -- we're much better off in terms of service disruption with a "classic" upgrade (upgrade secondary, reload peer, force failover, etc). 

Cisco advised us that it is unlikely that ISSU on 7600/6500 will meet our requirements, and hence we are better off doing classic upgrades. We've taken their advice, and will not be trying it again. I think it's suited for deployments where you have 30+ boxes that are identical in terms of configuration, and hardware, but in the SP environment (like us), the variance of boxes means that it's just not worthwhile.


Kind regards,
Rob

-- 
Rob Shakir                      <rjs at eng.gxn.net>
Network Development Engineer    GX Networks/Vialtus Solutions
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