Learn advanced techniques for managing RAID volumes in macOS Sierra. The Terminal commands include creating nested RAID arrays, adding hot spares, and checking the status of rebuilt volumes.
RAID arrays are quite common in enterprise environments and continue to grow in popularity in the SMB market. RAID arrays can be widely found in various industries, including digital media, finance, and legal practices.
The benefits of configuring a RAID array are immediately felt with the data performance and/or backup protection schemes in place. The ongoing management of a RAID set will change depending on the hardware utilized and the organization's needs; this may encompass removing faulty disks from an array, nesting arrays to provide additional redundancy against failures while maintaining high-throughput for I/O tasks or converting between arrays, as needed.
SEE: Data Backup Policy (Tech Pro Research)
Creating a nested or "stacked" RAID set
Nested RAID sets, such as RAID 10 for example, require two sets of mirrored arrays, which are then striped together for redundancy and performance. If mirrored sets are not available, they must be created before proceeding to the next step. If mirrored sets are available, enter the following command to identify the Unique IDs for each of the mirrored sets.
diskutil appleRAID list
The next command will create a striped RAID array from the two mirrored sets, which will result in a single volume to read/write from in macOS while your data is being copied to the striped array.
diskutil createRAID stripe RAID10_Volume_Name JHFS+ UUID_OF_MIRROR_ARRAY1 UUID_OF_MIRROR_ARRAY2
How to check the status of a mirrored RAID rebuild
Launch Terminal and execute the following command.
diskutil appleRAID list
The on-screen output will display all the RAID sets currently detected on the Mac. Listed next to the disk's UUID, a numerical value will appear under the Status column to denote the percentage complete during the rebuild process.
How to add a hot spare to a RAID array
With the Mac powered off, install a new hard drive or replace an existing failed drive. Launch Terminal and execute the following command to obtain the UUID of the new disk.
With the UUID of the hard drive, we can now add the HDD as either a spare or a member disk of the RAID array. The spare drive will automatically enable autorebuilding for that RAID array so that in the event of a disk failure macOS will utilize that disk to rebuild the RAID and get it operating normally again.
diskutil appleRAID add spare UUID_OF_NEW_HARD_DRIVE UUID_OF_RAID_ARRAY
If the disk is added as a member drive, the disk will be added to the existing RAID array to increase capacity, performance, or redundancy.
diskutil appleRAID add member UUID_OF_NEW_HARD_DRIVE UUID_OF_RAID_VOLUME
- How to manage RAID volumes in El Capitan (TechRepublic)
- How to manage RAID volumes in El Capitan: An intermediate guide (TechRepublic)
- Why RAID 5 still works, usually (ZDNet)
- Why do we still rebuild RAID drives? (ZDNet)
- The limits of RAID: Availability vs durability in archives (ZDNet)
Have a better way to set up a RAID configuration or a simpler way to manage existing arrays? If so, sound off in the comments section below.