What an array is and why you might need one

An array in networking means connecting multiple devices in a pattern that spreads data across them instead of sending everything through one cable or switch. The most common type you'll encounter is a RAID array — a set of hard drives or solid-state drives that work together to store the same data on multiple disks at once, or to split data across disks so that if one fails, you don't lose everything.

If you're running a wired network at home or in a small office, you might want an array to protect files you depend on — security camera footage, backups of work documents, or media libraries. A wired network gives you the speed to move large files to and from an array quickly, which is why people often pair the two together.

Arrays are not the same as straightforward external hard drives. An array is a system where the drives talk to each other and follow rules about how to store data. That coordination is what makes them useful for protection and speed.

Key Takeaways

  • RAID 1 (mirroring) copies your data to two drives, so you keep working if one fails, but you use twice the storage space.
  • RAID 5 spreads data and recovery information across three or more drives, so you lose less storage space but need at least three drives to start.
  • You need a RAID controller — either built into your motherboard, a separate card you install, or a dedicated box called a NAS — to manage the array.
  • Setting up an array means choosing your RAID level, installing the drives, and telling the controller how to organize them before you add any files.
  • A wired connection to your array is much faster than Wi-Fi, especially if you're moving large files or backing up many devices at once.

RAID 1: Mirroring for simplicity and safety

RAID 1 is the simplest array to understand and set up. You take two identical drives — two 2TB drives, for example — and the system writes the same data to both at the same time. If one drive fails, the other one has a complete copy, and you keep working without losing anything.

The trade-off is storage space. Two 2TB drives in RAID 1 give you 2TB of usable space, not 4TB, because one drive is always a backup copy. That's why RAID 1 works best when you have a small amount of data that matters a lot — financial records, family photos, or client files — rather than a large media library.

RAID 1 is also the easiest to recover from if something goes wrong. If a drive fails, you can pull it out, replace it with a new one, and the system copies the data from the surviving drive to the new one automatically. You don't need special recovery software or technical knowledge.

RAID 5: More storage, more complexity

RAID 5 spreads your data and recovery information across three or more drives. Instead of copying the whole file to a second drive, it breaks the file into pieces and stores recovery math on the drives so that if any one drive fails, the system can rebuild it from the pieces and the math.

The benefit is storage space. Three 2TB drives in RAID 5 give you about 4TB of usable space instead of 2TB. Four 2TB drives give you about 6TB. The more drives you add, the more efficient RAID 5 becomes — but you always need at least three drives to start, and you lose the space of one drive to recovery information.

RAID 5 is slower to set up and slower to recover from if a drive fails. When a drive dies, the system has to rebuild it from the pieces on the other drives, which can take hours or days depending on the drive size. During that time, your array is running without protection — if a second drive fails while the rebuild is happening, you lose everything. For that reason, RAID 5 works better when your drives are reliable and you're not in a hurry to recover.

Choosing a RAID controller

A RAID controller is the piece of hardware or software that manages the array — it decides which data goes on which drive, watches for failures, and rebuilds drives when they fail. You have three main options.

The first is a controller built into your motherboard. Many modern motherboards have RAID support in the BIOS, which means you can set up an array without buying anything extra. You plug the drives into the right ports on the motherboard, restart the computer, go into BIOS setup, and tell it to create a RAID 1 or RAID 5 array. This works for small arrays at home, but it uses your computer's processor to manage the array, which slows down other work.

The second is a separate RAID card you install in a PCI slot inside your computer. Cards like the LSI MegaRAID or Adaptec have their own processor, so they handle the array work without slowing down your main computer. They cost $100 to $500 depending on how many drives they support and how fast they are. This is the choice for people who want speed and don't want to tie up their main computer.

The third is a NAS (network-attached storage) box — a dedicated computer that holds the drives and connects to your wired network. A NAS has its own processor, its own power supply, and its own operating system. You set it up once, plug it into your network, and then any computer on that network can read and write files to it. NAS boxes range from $200 for a straightforward two-drive model to $2,000 or more for a four-drive or eight-drive model with fast processors. They're the best choice if you want to back up multiple computers or if you want the array to keep running even when your main computer is off.

Setting up a RAID array step by step

The exact steps depend on whether you're using a motherboard controller, a RAID card, or a NAS, but the general process is the same.

First, gather your drives. Make sure they are the same size and speed — mixing a fast new drive with an old slow one will slow down the whole array to match the slowest drive. For RAID 1, you need two drives. For RAID 5, you need at least three.

Second, install the drives in your computer or NAS. If you're using a motherboard controller or RAID card, open the computer case, find the right slots, and push the drives in until they click. If you're using a NAS, the drives usually slide into bays on the front or back of the box.

Third, tell the controller to create the array. If you're using a motherboard controller, restart the computer, press the key to enter BIOS (usually Delete or F2), find the RAID section, and create a new array. If you're using a RAID card, the card usually has its own setup program you access by pressing a key during startup. If you're using a NAS, you log into its web interface through your web browser and create the array from there.

Fourth, wait for the array to initialize. The controller will write the initial data structure to all the drives, which can take a few minutes to an hour depending on the drive size. Don't turn off the computer or NAS during this time.

Fifth, format the array with a file system. Once initialization is done, the array looks like a blank hard drive. You need to format it with a file system — NTFS if you're using Windows, ext4 if you're using Linux, or APFS if you're using macOS. This is the same process as formatting a regular external drive.

After that, the array is ready to use. You can copy files to it, back up your computer to it, or set it up as shared storage on your network.

Connecting your array to your wired network

If you're using a NAS, connecting to your network is straightforward: plug an Ethernet cable from the NAS into your network switch or router, and it appears on your network automatically. Any computer on the same wired network can see it and read files from it.

If you're using a RAID card or motherboard controller inside your computer, the array is only available to that one computer unless you share it over the network. To do that, you right-click the array drive in Windows File Explorer, choose "Share with," and pick "Specific people." Then you type the names of other computers or users on your network that you want to give access to. On macOS, you go to System Settings, find Sharing, and turn on File Sharing, then add the array drive to the list of shared folders.

A wired connection is much faster than Wi-Fi for moving files to and from an array. If you're backing up a computer with 500GB of files, a wired connection might take 2 to 4 hours, while Wi-Fi could take 8 to 12 hours or more. That's why people often set up arrays on wired networks — the speed makes the backup or file transfer practical.

When an array drive fails and how to replace it

If a drive in your array fails, the controller will alert you — usually with a light on the drive bay, a message on the NAS screen, or a notification on your computer. The array keeps working (in RAID 1, you have a full copy on the other drive; in RAID 5, the system can rebuild from the pieces), but you need to replace the failed drive soon.

To replace a drive, power off the array or NAS, pull out the failed drive, and slide in a new one of the same size or larger. Power it back on, and the controller will automatically start rebuilding the array — copying data from the surviving drives to the new one. This can take hours or days depending on the drive size. Don't turn off the array during the rebuild, and don't remove any other drives.

Once the rebuild is complete, the array is protected again. If you're using RAID 1, the new drive is now a full copy of the other one. If you're using RAID 5, the recovery information is spread across all the drives again.

Frequently Asked Questions

Do I need an array if I just want to back up one computer?

Not necessarily. A single external hard drive is simpler and cheaper. An array makes sense if you want protection against drive failure — so that if the drive dies, you don't lose your backup — or if you're backing up multiple computers and want them all to write to the same place at the same time.

Can I use drives of different sizes in the same array?

Technically yes, but it's not recommended. In RAID 1, the array will only use as much space as the smaller drive, so a 2TB drive paired with a 4TB drive gives you only 2TB of usable space. In RAID 5, the array treats all drives as if they were the size of the smallest one. It's better to use matching drives.

What happens if two drives fail at the same time in RAID 5?

You lose all your data. RAID 5 can recover from one drive failure, but not two. That's why RAID 5 is riskier than RAID 1 — you have only one layer of protection instead of two. If drive failures worry you, use RAID 1 or RAID 6 (which can survive two failures but requires at least four drives).

Is a NAS better than a RAID card inside my computer?

It depends on what you need. A NAS is better if you want to back up multiple computers, if you want the array to keep running when your main computer is off, or if you want to move the array to a different computer later. A RAID card is better if you want maximum speed and you only need the array on one computer.

How often should I check on my array?

Most controllers send you an alert if a drive fails or if something goes wrong, so you don't need to check constantly. But once a month, it's worth logging into the NAS or checking the RAID status in your computer to make sure all drives are healthy and the array is rebuilding normally if a drive has failed.