Mirroring, as discussed in this manual, is a database server feature. Your operating system or hardware might provide alternative mirroring solutions.
If you are considering a mirroring feature provided by your operating system instead of database server mirroring, compare the implementation of both features before you decide which to use. The slowest step in the mirroring process is the actual writing of data to disk. The database server strategy of performing writes to mirror chunks in parallel helps to reduce the time required for this step. (See Disk Writes to Mirror Chunks.) In addition, database server mirroring uses split reads to improve read performance. (See Disk Reads from Mirror Chunks.) Operating-system mirroring features that do not use parallel mirror writes and split reads might provide inferior performance.
Nothing prevents you from running database server mirroring and operating-system mirroring at the same time. They run independently of each other. In some cases, you might decide to use both the database server mirroring and the mirroring feature provided by your operating system. For example, you might have both database server data and other data on a single disk drive. You could use the operating-system mirroring to mirror the other data and database server mirroring to mirror the database server data.
Logical volume managers are an alternative mirroring solution. Some operating-system vendors provide this type of utility to have multiple disks appear as one file system. Saving data to more than two disks gives you added protection from media failure, but the additional writes have a performance cost.
Another solution is to use hardware mirroring such as RAID (redundant array of inexpensive disks). An advantage of this type of hardware mirroring is that it requires less disk space than database server mirroring does to store the same amount of data in a manner resilient to media failure. The disadvantage is that it is slower than database server mirroring for write operations.
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