When data is being backed up, a common technique used to help add redundancy is called mirroring. This technique allows the user to simultaneously write data to two different storage devices at the same time. This allows for the data to be backed up in two different locations at once, instead of manually backup the data up to a different storage device at a different time.

Mirroring is used to provide a backup drive to one that may otherwise have failed. For example, if one of the mirrored drives fails when someone is trying to access it’s data, the other mirrored drive acts as a backup and can continue feeding data where the other one left off. If need be, the failed drive can then be replaced and then can be set to mirror the non-failing drive. However, if for some reason both drives were to go out, then I guess you’re just out of luck (unless you mirrored on three different drives).

Another type of data backup similar to mirroring is known as duplexing. This method not only makes a dual backup of data such as mirroring does, but it also backups up the host I/O controllers, which are responsible for handling the data. With mirroring, if your host controller fails, then you won’t be able to access the data until the controller is replaced. If you used the duplexing method, however, a backup of the I/O controller is made and because of this you should still be able to access the data. All in all, while duplexing makes for a more secure backup, sometimes you just won’t find a need for backing up your host I/O controller, and mirroring data is more logical in that situation.

There are two different types of mirroring in use. The first type is software mirroring, where software is used in order to mirror information. This type of mirroring is cheaper than it’s alternative (hardware mirroring), but at the cost of speed. Software mirroring tends to be a bit slower than then max speeds reached by hardware mirroring.

The alternative, as previously mentioned, is hardware mirroring. Hardware mirroring, also known as disk mirroring, is handled by the hardware on the host computer. This computer’s hardware is designed to write the data twice, so naturally is more efficient than software mirroring because it is running on a lower level of operation (hardware level), as opposed to running on the software level, where things aren’t as efficient. Hardware mirroring can also be handled by an external storage device itself, where the host computer then has nothing to do with the mirroring of data.

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