RAID drives
Combine drives to keep your data safe
RAID (Redundant Arrays of Independent Disks) offers a way to keep your data safe through combining multiple
drives. Although RAID isn’t intended to be a backup solution in itself, keeping multiple copies of your data across various hard drives means that your information is safe if any one drive fails.
In this section, we’ll explore the various types of RAID setup, as well as how to use macOS’s Disk Utility to set up a RAID array of your own using regular external drives.
RAID levels
RAID can be set up in several ways, known as RAID levels. When it comes to making sure your data is safe, the best kind is mirrored (known as RAID 1). At its very simplest, this involves two disks which mirror the contents of one another exactly, as data is written. This is a little different to backup facilities such as Time Machine, which perform scheduled backups at certain times of day. A RAID setup has an advantage over cloud-based storage services as it can mirror your drive exactly without requiring an internet connection.
The simplest way to get started is to buy an external RAID drive, such as those available on the online Apple Store. Custom-built RAID devices often come with a specialist RAID controller chip, which will generally offer the very best performance, as a separate computer is essentially running the RAID itself, freeing up resources on your Mac. This can be expensive, however, and is usually unnecessary for a home or small business. The alternative is to set up and use a software-based RAID array that’s managed by macOS. (See the walkthrough below.)
In order to get started, you’ll need two or more hard drives to connect to your Mac. In a mirrored setup, data is copied exactly, bit for bit, so your RAID array’s capacity will only be as large as the smallest disk in it. Check the data access speeds for all disks carefully too, as the read/write speeds of your array will also be determined by its slowest disk.
There’s no hard limit on the number
In a mirrored setup, data is copied exactly, bit for bit
or type of disks you can use but try to avoid using several from the same manufacturer in case they both have the same design flaw. Some RAID devices will only accept replacement disks from their manufacturer. Check with the manufacturer to find out which specific models of disk are supported.
If you choose to use Disk Utility to create a mirrored RAID array of two disks, each one is a RAID slice; content is written exactly the same, in real time, to both disks. If you set up a mirrored array that contains more than two disks, you can choose to set up one or more of the extras as a RAID spare.
A RAID spare exists as a kind of backup drive. Content isn’t automatically written to the spare when you use your array, but if one of the RAID slices fails, the array’s data is written to one of the spares to take over from the failed slice.
When setting up your RAID array, you’ll be asked to set its chunk size. In a RAID setup, data is broken down into pieces and written across two or more disks. The chunk size allows you to set the size of those pieces.
Generally speaking, if you’re not using your Mac for working with very large files, such as for video editing, it’s safe to choose the default chunk size in Disk Utility, which is 32K.
Seeing RAID
Once your RAID setup is complete, you’ll notice that Disk Utility and Finder will see the array as one drive. This means, for instance, that you can configure Time Machine to use it for backups.
You can also run the RAID Assistant as many times as you wish, so feel free to add more drives to your setup and/or replace them as time goes on. Most modern solid-state drives will display a warning as they near their end of life, if you open Disk Utility and use the First Aid feature.
Remember that although you are storing data across multiple drives, they will most likely all be in the same place. This leaves them vulnerable to damage or theft. Try keep at least one off-site backup of your data. You might create this by using software such as Carbon Copy Cloner to copy the contents of your RAID array to a separate external hard disk, and you can then store this somewhere else that’s secure.