Re: [Ganglia-developers] Python multi disk implementation

[<Dan...@ba...>]

 
> > - How should such a module handle disks that are not always 
> present, 
> > e.g. iSCSI SAN volumes attached after the process has 
> started?  Is it 
> > appropriate to re-initialise the list of metrics while gmond is 
> > running, or is it necessary to restart the entire gmond 
> process each 
> > time disks (or NICs) are attached/detached?
> > 
> 
> In the current implementation, gmond will have to be 
> restarted in order to recognize new disks.  I have looked 
> into a way for the metrics list to be reinitialized on the 
> fly, but haven't been able to come up with a good 
> implementation.  Part of the problem is that any new metric 
> also requires a configuration file change.  There would have 
> to be some way for either a module or a user to poke gmond 
> and tell it to re-read the configuration file and then 
> reconstruct the metrics list without dropping any of the in 
> memory data.  I am guessing that a robust implementation will 
> probably also include some way of generalizing the 
> Collection_Group configuration section so that each metric 
> does not have to be listed individually.  The set of enabled 
> metrics would somehow have to be generated on the fly.  
> 


How about metric instances, e.g. if the metric is the number of IO
reads, there could be an instance for each volume.  All of these
instances might share the same name and/or index, but have some kind of
sub-index for each instance (e.g. hda, hdb)

Such a scheme would need an additional discriminator field in the XML,
and gmetad might have to split the rrds into sub-directories.

Regards,

Daniel

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