Mirroring and redundancy are related concepts in data storage, particularly in disk groups, but they refer to different aspects of data protection and fault tolerance. Based on the provided reference, redundancy level defines the overall fault tolerance of a disk group, while mirroring levels specify how individual files are initially duplicated.
Understanding Mirroring vs. Redundancy
In the context of disk groups and data protection:
- Mirroring Level: This refers to the configuration setting that dictates how data is duplicated when files are created. Default mirroring levels apply unless a different level is specifically designated for a file. It's about the method or degree of data duplication for file creation.
- Redundancy Level: This is a measure of the overall fault tolerance of the disk group. As stated in the reference, the redundancy level controls how many disk failures are tolerated without dismounting the disk group or losing data for specific disk group types like normal and high. It defines the outcome or capacity to withstand failures.
Essentially, mirroring is a technique or level used to duplicate data, contributing to the broader goal of achieving a specific level of redundancy, which is the measure of how many failures the system can survive.
How They Relate
Mirroring levels configure how files are written with copies, which in turn helps the disk group achieve its defined redundancy level. For example, a higher mirroring level for files would typically contribute to a disk group's ability to tolerate more disk failures, thus achieving a higher redundancy level.
Let's look at the distinction:
| Feature | Mirroring Level | Redundancy Level |
|---|---|---|
| Scope | File creation (default setting) | Disk group (overall protection) |
| Purpose | Define data duplication for files | Define overall fault tolerance |
| Measurement | Levels (e.g., normal, high) | Number of disk failures tolerated |
| Result | Data copies for files | Ability to survive disk failures |
| Based on Ref. | Default setting for file creation | Controls tolerance to disk failures |
Practical Insight
Consider a disk group set up for "normal" redundancy. This redundancy level might dictate that the disk group can survive one disk failure. To achieve this, the system might use certain mirroring levels when creating files by default (e.g., mirroring data onto two disks). If you were to specify a lower mirroring level for a particular file, that specific file might not be as protected, but the overall disk group's redundancy level (ability to tolerate X failures) is still governed by the disk group's configuration.
In summary, mirroring levels are about how data copies are made for files, contributing to redundancy, which is the measure of how many disk failures the entire group can withstand.
