The Need for Logical Volume Managers
There are two ways to implement RAID within disk arrays. Hardware, or controller-based, RAID is implemented via firmware in the disk array. Software, or host-based, RAID is implemented via software on the host server. Of course, you can combine the two methods as well.
While it may seem that RAID via hardware would be preferable, there are some drawbacks. Often this approach requires a one-time, static configuration. If the DBA guesses wrong or if the application I/O patterns change over time, the only solution is to back up the data, reconfigure the array, and reload the data. For a multi-terabyte data warehouse, this exercise could take an entire weekend! Another issue is that different RAID configurations ...
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