From: Chad Martin
Date: July 13 2005 6:07pm
Subject: Re: evaluation of mysql cluster (comparison with oracle rac cluster)
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Martino Piccinato wrote:
> 4) Storage space scalability. Full replication on a "shared nothing"
> cluster has a shortcoming in available storage space as every new node
> added must have at least as much space as the other nodes. This might
> not be a problem for a x*10GB database but can become very expensive for
> a x*100GB (many disk for every node) and really difficult for a TB
> database: Whether you add shared storage or raid disks you have to fully
> duplicate the entire DB storage for every single server.

I don't understand this.  What do you mean by "full replication"?  You
seem to imply that everytime you add a node to a MySQL Cluster, you bump
up the number of replicas by one.  That's not how you do things, since
that totally kills the scalability of it.  You set your number of
replicas at 2 or 3 and add nodes as your storage/performance demands
dictate.  Your last sentence above is totally false.  Read up on Cluster
a little more.

>> - Third, due to the fact of having a physical data partition to node
>> relationship, shared nothing systems are not flexible at all to adapt to
>> changing business requirements. When the business grows, you cannot
>> easily enlarge your system incrementally to address your growing
>> business needs. You can upgrade all existing nodes, keeping them
>> symmetrical and
>> avoiding data repartitioning. In most cases upgrading all nodes is too
>> expensive; you have to add new nodes and to reorganize - to physically
>> repartition - the existing database. Having no need for reorganization is
>> always better than the most sophisticated reorganization facility.

This is true as long as you're more concerned with time lost due to data
repartitioning as opposed to time lost due to hardware failure downtime.
 It kinda depends on your priorities.

>> - Finally, shared nothing systems, due to their use of a rigid
>> restricted access
>> scheme, fail to fully exploit the potential for high fault-tolerance
>> available
>> in clustered systems.

What?  Are they claiming that have a single point of failure is more
fault-tolerant?

Chad Martin
Arete Studios, Inc.