When I tried to explain what a cluster is, I came up with a very simple explanation that gives an idea of what a cluster can be without all of the technical stuff. Just to give you this example:
Try to think of a car manufacturer that has sites in two locations. Both have the capability to build cars, but only one site is active at a time. Now you as a customer want to be able to communicate with this company no matter where they are currently working from. The way to do so would be a P.O. box. The active site just picks up the mail from this box and corresponds with you.
Say for example that one site would burn down, the other would take over and correspond with you using this P.O. box, and to you as a customer the "failover" to the other site would not be noticeable.
I know this doesn't cover all aspects, but it is very effective way to describe the very basics of a cluster. Anybody can imagine a P.O. box and someone driving to pick up the mail from that box.
Now, at the company where I work we tend to use three main products for our clustering needs. The Microsoft Cluster Service for our Windows platforms, We use a custom created product called PMC (very basic, two nodes with manual failover) and EMC Autostart. All provide a basic failover functionality of shared resources, and usually some means to stop and start things like databases and applications.
All of the people here seem to answer one thing when you ask them about high availability. "Install a cluster" seems to be the common delimiter. But when you ask them what they think when it comes to high availability you get all sorts of replies. Raging from "never down" or "100% reachable" to "guaranteed fast response times" or even the cloning of the runtime instance to other machines.
All are (in my opinion) quite valid responses, but there is one thing that I have learned over the past few years: The more complex the demands, the more stable your environment will be if you keep your design and implementation as simple as possible. Or in short "KISS".
Requirements that are quite popular are for example "I want to monitor the response time of my database query", or "The SAPgui interpretation time should be under $X". Very much like in the uncertainty principle we can say that as soon as we start to measure the response times of the database, we are also going to have an impact on these response times. And the more complex the demands are, the more you need to take in to account and the higher the costs are going to be. Sun has a nice image displaying this, and it is a general image you will see when you are searching for HA-clustering.
My advice? Try to keep it down to a minimum.
Rely on your hardware redundancy. You can use the N+1 principle there and usually save quite a bit. Also, make sure that the people who are working on the cluster know what they are doing. I've seen most errors here start off by either poorly defined monitors, too many monitors and user error (or PEBKAC).
In short, a cluster is alway complex and tailored toward the application you are trying to make highly available. Keep the design as simple as you can and gather people around you with knowledge of the application so you so can define a good set of working guidelines and monitors. All in all, a case of "KISS".
People are not panicking, but some are not far from it as it seems. The open source community had big concerns about MySQL even though Oracle is also responsible for a storage engine that is actually distributed with MySQL.
What I found much more interesting was taking apart the various pieces that Sun provides through this acquisition and what Oracle could bring when taking current trends and "buzzwords" into account.
One of the trends that was seen throughout last year was SaaS, "green IT" and the word of the year 2009 is most likely "cloud". The strange thing is nobody has a clear knowledge of what either is, but almost every company out there will show various implementations of these terms.
So, what if Oracle puts it all together? Just stay with me for a second. They have, among others, their own business suite. They have a database, they now have an operating system that will probably be modified to ensure a smooth cooperation between everything. Then you've got the xVM Ops center that allows you to use the virtual machines that you created. They can even use their own hardware.
What would happen if oracle gives the idea that SAP had with their business by design a thwirl? They could have their own cloud, you could order your application to go. As you expand you could purchase a sort of middleware box that connects beautifully to the Oracle cloud. And should you go even bigger, then you can purchase the consulting from them that helps you migrate everything to your own location, and you could again get everything from one supplier.
It's not something easily made, but Oracle now has the theoretical potential to deliver in each configuration you would choose.
Any thoughts on this? Am I just rambling? Looking forward to the comments!
To start my first post I need to get something off my chest. Anyone who has been involved with SAN has probably noticed the launch of the new Virtual Matrix Architecture (or in short V-Max) by EMC last Tuesday.
I am still busy trying to gather all of the information and filling in the blanks that still exist for me. Anyway, all in all to me the solution so far looks pretty good and will need to prove itself in terms of scalability and such.
What really bugs me though is the reaction of some competitors (actually, at this moment only one competitor). The culprit? Hitachi Data Systems or in short HDS.
And why you might ask? Well, to me it seems that they felt the need to respond quickly. At least they did so, I'll give them that much. But instead of replying they tried to start a good old flame war. All of the classic signs are there. No knowledge of the matter was pretty poor and they tried to score by fussing over the name of the product.
All in all, as a customer and end-user of the various SAN solutions I have to say that the replies made by the various HDS people made me feel less likely of possibly purchasing a USP-V from them.
Me, I like to see products that solve the problems that I have in a reliable way. Be it from an infertile tiger or from an electronics repair shop. I just need to get the job done, what do care about the name?