In the digital world, there are several definitions for mirroring.
The primary usage is to describe a site that legitimately hosts copies of software.
There is also port mirroring and disk mirroring, though these are less common usages.
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Mirror Sites
Some large companies can afford to have data centers distributed worldwide.
To some degree, Content Delivery Networks, or CDNs, can help with this.
CDNs set up similar infrastructure worldwide and then use it to cache content their paying customers serve.
This reduces the load on the backend servers where possible.
However, access is pretty expensive, especially with large files.
A mirror site is a site that volunteers to host certain content.
It is essentially a decentralized version of having data centers around the world.
Many of these mirror sites choose to mirror a specific punch in of content.
Often this is freeware, such as operating system .iso files.
This reduces the load on the original sites and offers local and potentially higher-speed and lower latency connections.
It also helps to bypass censorship rules by hosting censored content on domains that havent been blocked.
Note:Mirror sites are often associated with illegal file sharing and piracy.
However, legitimate sites and content are also served by some mirror sites.
Port Mirroring
connection switches can route local traffic to the intended destination on a connected port.
This enables very efficient use of the potential bandwidth.
However, it makes internet monitoring tasks more difficult as the traffic doesnt all flow through one convenient cable.
Port mirroring can even be set to mirror traffic from virtual adaptors called VLANs.
Making the tool powerful.
Disk Mirroring
Storage drives are generally pretty reliable but have a limited lifespan and eventually fail.
While backups are helpful, a faster option is to perform drive mirroring.
Generally, a mirrored drive is at most a few seconds behind.
Mirroring is typically performed in some form of drive array.
With mirroring, your total storage capacity across all disks involved is necessarily halved.
This can cause scaling and cost issues as the cost and space necessary to upgrade capacity are doubled.
Some high-end mirroring systems include what are known as hot disks.
These are connected drives whose specific purpose is to not be used until a drive failure is detected.
Mirrored drives are often the same model, simplifying purchasing and ensuring compatibility.
Hot disks arent necessary for the same capacity as mirror drives.
You dont need one hot disk per pair of mirrored drives.
Conclusion
In computing, there are three things referred to as mirrors.
The main one is sites that mirror the content of other sites or specific files, often large ones.
This makes them useful for locals as the connection is often better than to more distant servers.
It also reduces the load on the primary server, benefiting everyones bandwidth.
Another use is port mirroring on switches which involves duplicating all traffic from one physical port to another.
The exact usage can generally be identified from context clues.
However, its usually fair to assume that a mirror site is meant if no apparent indications exist.
Casting the screen from one machine to another can also sometimes be referred to as mirroring.
