Craig S. Mullins

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February 2003

 

 

 

                                           



The DBA Corner
by Craig S. Mullins  

 

DBAs Do Storage Management

Since the DBA deals with database management systems that store data, a good part of the DBA's job will involve planning for the actual storage of database data. As a rule, DBMS vendors do not certify or explicitly support any specific third party storage products. Instead, the assumption is made that some underlying storage technology is available and will be reliable. The DBA must evaluate the many products, technologies, and vendors that provide storage solutions to determine what will work best with each DBMS. Fortunately, most storage technologies can work with most DBMS products. The predominant storage technology used for data management is the disk drive. Modern disk drives are more reliable than in years past with an ever-increasing Mean Time Before Failure (MTBF). It is not unheard of for disk drives to achieve in excess of 100,000 hours of availability before failing. But the mechanical nature of the disk drive renders them more vulnerable to failure than other computer component. As the number of disk drives in a system increases the vulnerability increases. Certain modern storage solutions, such as RAID, can be used to address some of the MTBF problems.

For mission critical applications, data integrity can be more important than data availability. If the storage media is unreliable and a failure causes data corruption, the lost data can be more of a problem than the downtime. It is imperative that database storage solutions protect the data.

Database performance is I/O dependent - the faster the DBMS can complete an I/O operation the faster the database application will run. Remember that data retrieval from storage media takes much longer to complete than data retrieval from cache or memory. For this reason, some modern storage systems provide their own caching mechanism to pre-stage data in memory - thereby reducing the wait time associated with traditional disk I/O operations.

Indeed, storage is becoming more central to business operations. Heterogeneous, multi-terabyte, database sites are not uncommon these days. The amount of data being stored is greater than ever before, and data is being stored for longer durations, too. One company, Winter Corp., specializes in VLDB (Very Large Database) issues. In its most recent survey of the largest databases in the world Winter Corp. projects a 100 TB database by 2005. Additionally, the report documents several very large databases including a 10.5 TB Unix-based data warehouse and a 1.45 TB Windows NT-based data warehouse.

For the DBA, this growth in storage capacity further increases the complexity of managing data and databases. Many organizations are implementing new storage technologies, such as Network Attached Storage (NAS) and Storage Area Networks (SANs), to help manage the ever-increasing amount of storage required for modern applications. Goals to consider while building a storage system for your database include: preventing loss of data; assuring that adequate capacity is available and that the storage solution can easily scale as storage needs grow; selecting a solution that provides fast access to data with minimal, or no interruptions to service; choosing storage solutions that are fault-tolerant and that can be repaired rapidly when a failure occurs; selecting a storage solution where you can add or replace disks without taking an outage; and combining all of the above into a cost-effective storage solution that is within a budget your company can afford.

Finally the DBA and the storage administrator will need to cooperate to facilitate proper database storage. Indexing, partitioning, clustering, and separation of data will cause the database to require more storage (and across more drives) than most storage administrators anticipate. The DBA will need to clearly explain how much storage is required for the database. The better the DBA communicates, and the better the relationship is between these two IT professionals, the better your database applications will perform. And that is what it is all really about.

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From Database Trends and Applications, February 2003.

2003 Craig S. Mullins,  All rights reserved.

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