Make and manage disk sets
Combine disks for faster transfers or to provide extra protection for files
REQUIRES
macOS Sierra
you will learn
How to set up a striped or mirrored disk set using macOS’s RAID support in Disk Utility
IT WILL TAKE
10 minutes
Disk Utility in macOS 10.12 Sierra adds the ability to create and manage disk sets. (Strictly speaking, you could also manage disk sets in OS X 10.11 El Capitan, but you had to do it using the not exactly user-friendly “diskutil” command in Terminal.) A disk set requires multiple hard disks – a minimum of two – and pools their storage in one of three ways. The first is a “striped” disk set, or RAID (Redundant Array of Independent Disks) level 0. This type of set combines the capacity of all its disks into one big pool, but it spreads “chunks” of data, even if they’re part of the same file, across its disks to speed up read and write operations, improving the set’s overall performance. However, the risk here is that if just one disk fails in the set, you may lose data permanently.
the good type of redundancy
The second type is a mirrored disk set, also known as RAID level 1, and for many people it’s the most attractive option due to the additional protection it gives your files; whatever you copy to a mirrored set is stored multiple times – once on each of the disks in the set.
The advantage of this is that as long as only one disk fails, you can rebuild the setup by replacing the faulty drive. The worst case here is if data on every disk becomes corrupted, or all of the disks fail at the same time. The former situation can be addressed by creating one or more periodic backups of the mirrored set and storing that separately.
The latter situation can be dealt with by adding one or more extra disks to the set – either as additional “slices” (live copies of all the data stored by the set) or as spares. These are usually idle, and are only called into action when another slice fails, so that the setup can be rebuilt with your data still stored on multiple drives.
A mirrored disk set’s capacity is equal to the lowest capacity disk that’s part of it, so you’ll want them to match in order to make the most efficient use of storage.
The third kind of disk set is JBOD: “just a bunch of disks.” This simply adds the capacity of multiple disks – which can be different – into a single volume. This kind of disk enables several small disks to work as if they were one bigger one.
In the walkthrough opposite, you’ll learn how to safely set up RAID 0 and RAID 1 disk sets. Before you begin, gather at least two drives that are blank or whose contents you don’t need; they will be erased, so make sure you have a backup of anything on them that you want to keep.