Storage : Pupose of the "Master" storage domain status

Latest response

Hello

 

I've been all through the official documentation but can find no information regarding the purpose or definition for the "Master" storage domain.

Would you be able to provide this ?

Particular questions I have are :-

 

What is its purpose ?

Is it manager, datacentre or cluster specific ?

Can you have mutliple Masters ?

What decides which SD should be Master ?

Can the Master status be moved/migrated between SDs?

 

Thank You

Responses

Taking it from the top, every datacentre, in storage terms, is a storage pool. A storage pool is a container of a set of storage domains, and storage-pool-wide operations are done by the SPM host.

 

Now, because of this grouping of storage domains, there should be a central location that holds the metadata fro the storage pool - which domains belong to it, how they can be reached and so on. The master SD is what holds this metadata in addition to it's own metadata, the non-masters do not hold pool-wide information, only their own metadata.

 

To move the master role, you can simply put the current master in maintenance mode, if there are additional data SDs available, the role will be migrated to the next available data domain.

 

> What is its purpose ?

 

See Dan's reply.

 

> Is it manager, datacentre or cluster specific ?

 

Datacentre.

 

> Can you have mutliple Masters ?

 

One master per dc.

 

> What decides which SD should be Master ?

 

I think it's random like assigning SPM role to hosts.

 

> Can the Master status be moved/migrated between SDs?

 

If you put master sd to maintenance another available sd will take the role. We don't have control to which sd to transfer the role. RHEV-M selects it.

Thank You, Gentlemen

Exactly what I required.