24x7 enterprise databases

Hi, I am Noel Yuhanna, an analyst at Forrester Research.Today I will be talking about 24x7 enterprise databases. What does it mean?Well, databases today are very critical in any organization, in banks, ininsurance companies. And you have to ensure availability of these databases.How do you ensure it? Databases could fail.

There could be multiple reasons why a database failsactually. Three of the most common ones we know of are hardware failures,software failures and human error.

Software failures account for 30% of all failures whereashuman errors account for only 15% of all failures. The biggest portion of thesefailures are accounted to hardware failures, which is 55%.

Let's look at the reasons why hardware failures can happen.When an application goes down, there can be reasons why it goes down. It couldbe a network failure or it could be a server failure or a storage failure.

There could be four different solutions available, to helpyou with availability. One is replication. In a typical environment you wouldhave an application connected to a database and to a server and you may haveanother database and another server available in different locations. And whatyou want to do is replicate data. Whenever transactions are coming into to oneserver you want to replicate to another server, to make it available so that ifone server goes down, the second server can make it all available.

Well there are some limitations however with thistechnology. All data might not be available to the second server. There couldbe some latency there. So you may lose transactions around these applications.So it is a good technology, easy to implement, but may not serve the purpose ofcomplete availability.

The second solution we know of is shared nothing clustering.Now this is a good technology, which you can have a segregation of data, whichreally splits the data or breaks down the data into multiple chunks. Some datamay be stored in this database, some data may be stored in this database aswell and both of them together deliver information toward the application.

Now there could be the possibility that with one server andapplication or the database may go down. What do you do? Well your data may notbe completely available, so there are some limitations as well with thistechnology.

The third technology which we know of is shared diskclustering. How shared disk clustering actually works is that one applicationconnects to a database and to a server and to a storage. And the second serveris just a standby, just being available if at all necessary. And there iscommunication going on between the server and server to understand where doesthe issue lie, if the server is available or not. If the server goes down forsome reason this other server will pick up the data and make it available to theapplication. So this is a good technology, but may again take you some time toget to that situation. It may take five minutes to seven minutes to recover thedata and make it available to the application.

The fourth solution that we know of, which is actually anevolution of the shared disk clustering is called the multi-node-clustering.How the multi-node-shared-disk clustering works, is that the applicationinteracts with the database which has multiple servers associated with it andall these servers tie to a common storage. So all of them deliver the same typeof information available to the application.

Now the good thing with this technology is that if at all aserver goes down, your other servers are available, and serving theapplication. In fact you can have more servers if you require, to make itavailable as well. You can have 10, 16, 24 nodes, we call it nodes available inthis environment. So this is a good technology which serves a better purpose.It also delivers to you availability for the application as necessary. And wesee a growing trend where we see multiples of these low cost servers acting asa shared disk clustering solution.

To summarize, we looked at why databases fail. One of thereasons is hardware failures. We also looked at four different solutionsincluding replication, shared nothing clustering, shared disk clustering, andmulti-node shared disk clustering. To ensure availability of 24x7, the bestsolution that we know of is multi-disk node clustering. We believe multi-nodeshared disk clustering delivers the highest availability.