RAID (Redundant Array of Independent Disks) is a technology that combines multiple physical disk drives into a single logical unit to improve performance and/or reliability (Wikipedia). The first RAID systems were developed in the late 1980s to enhance server storage performance and provide fault tolerance (TechTarget). Over the years, different RAID levels have been developed with various combinations of performance, data protection, and cost.
Apple has supported hardware RAID in Mac computers since the early 2000s (Eclectic Light Co.). Their implementation allows combining the internal drive bays in a Mac Pro or hard drive slots in an Xserve to create a RAID array managed directly by macOS. Setup and management is done through Disk Utility or Terminal, without requiring a separate hardware RAID controller. Apple RAID provides an integrated way to implement RAID 0, 1, 5, 6 and 10 configurations.
RAID Levels Supported by Apple
Apple supports several types of RAID in Disk Utility and SoftRAID, including:
RAID 0 (Striping)
RAID 0 stripes data across multiple disks for improved performance, but offers no redundancy. According to Apple’s RAID Utility User’s Guide, RAID 0 is best used for audio/video streaming and editing where performance is crucial. However, data loss could occur if one drive fails.
RAID 1 (Mirroring)
RAID 1 duplicates all data across two drives for redundancy. The RAID Utility User’s Guide states RAID 1 provides good performance and complete data protection if a single drive fails. But it requires double the drive capacity for full redundancy.
RAID 5
RAID 5 stripes data and parity information across 3 or more disks. According to Lifewire, RAID 5 was supported in Disk Utility until OS X El Capitan. If one disk fails, data can be rebuilt from the parity information. RAID 5 offers a balance of redundancy, capacity efficiency, and performance.
RAID 10
RAID 10 is a nested RAID that combines mirroring and striping for redundancy and performance. As Lifewire mentions, direct RAID 10 support was removed in OS X El Capitan but can still be created manually. RAID 10 provides fast performance and can withstand multiple disk failures, but requires 4+ disks.
Hardware Requirements
Apple RAID requires certain Mac hardware and configurations to properly function. The primary requirements are:
- Compatible Apple Mac models: Xserve RAID, Mac Pro, Mac Mini Server, and Xserve servers are compatible with Apple RAID.
- Minimum RAM: At least 1GB of RAM is recommended, with 2GB or more being preferred for better performance (1).
- Minimum drive configuration: The minimum number of drives needed depends on the RAID level being implemented. RAID 0 requires at least 2 drives, RAID 1 requires at least 2 drives, and RAID 5 requires at least 3 drives (2).
Meeting these hardware prerequisites will enable Apple RAID to function optimally when creating and managing RAID arrays.
Setting up a RAID Array
Setting up a RAID array on macOS can be done using the built-in Disk Utility application or the command line. The easiest method for most users is through Disk Utility.
To set up a RAID array in Disk Utility:
- Open Disk Utility, located in Applications > Utilities
- Click on the drives you want to include in the array in the sidebar
- Click the RAID button at the top of the window
- Select your desired RAID level – RAID 0 for speed or RAID 1 for redundancy
- Give the RAID volume a name
- Click Create
- The RAID volume will now appear in the sidebar ready for use
For more advanced users, RAID arrays can also be created through the command line using the diskutil tool. This allows for additional flexibility and options not available in Disk Utility such as more RAID levels. Instructions can be found here.
Managing and Monitoring
Apple provides built-in tools for managing and monitoring RAID arrays on Mac computers. The primary utilities are Disk Utility and System Information.
Disk Utility allows you to view the status of your RAID arrays and the drives that make them up. You can check for any errors or issues that need to be addressed. Disk Utility displays the RAID type, status, and size for each array (Apple Discussions).
The System Information app provides more detailed stats and SMART status data on the physical drives in the array. This helps identify any potential disk errors or failures before they become a major issue. You can view drive temperature, power on hours, and other metrics (Apple RAID User Guide).
Third party utilities like SoftRAID also offer advanced RAID monitoring and email notifications when degradation is detected. This helps admins proactively maintain maximum uptime (SoftRAID).
Regularly monitoring RAID health using these tools is important to identify and address any problems early before data loss occurs.
Expanding a RAID Array
One advantage of Apple RAID is the ability to easily expand existing arrays by adding additional drives. This allows you to increase the storage capacity of your RAID array without needing to rebuild it from scratch.
To expand an existing Apple RAID array, first make sure the new drives you want to add are equal to or larger than the existing drives in capacity. Then install the new drives and launch Disk Utility. Select the existing RAID array in the sidebar and click the “Add Disk” button. This will initiate the expand process, adding the new drive to the array and increasing its total capacity.
According to Apple’s support documentation, expanding a RAID 0 array simply concatenates the new drive onto the end of the existing array, while RAID 1 and RAID 5 expand by adding the new drive and restriping existing data across all drives 1. The expand process can take some time to complete depending on the size of the RAID array.
It’s important to note that most other RAID implementations don’t allow on-the-fly expansion like Apple RAID. This feature makes it very convenient to upgrade storage capacity without needing to backup and rebuild the entire array.
Rebuilding a RAID Array
If a disk in a RAID 1 array fails, the array will go into a degraded state with reduced redundancy. Rebuilding the array by replacing the failed disk is crucial to restore full redundancy and protection against data loss. Here are the steps for properly rebuilding the array on a Mac:
1. Open Disk Utility and identify the failed disk indicated by an exclamation point icon. Unmount the failed disk if it is still mounted.
2. Physically remove the failed disk and replace it with a new disk of the same capacity or higher.
3. In Disk Utility, select the degraded RAID array and click the Rebuild button. This will initiate a rebuild onto the replacement disk.[1]
4. Monitor the progress until completed. Do not interrupt the rebuild process.
5. Once rebuilt, verify the status shows as Normal and redundant again. The data and RAID configuration will be restored.
Rebuilding as soon as possible after disk failure is crucial to avoid the possibility of a second disk failing, which would result in complete data loss. Regularly monitoring disk health can help detect failures early. Maintain spare standby disks to enable fast recovery.[2]
Migrating a RAID Array
When getting a new Mac computer, you may need to migrate an existing RAID array and retain the data. The process for doing this depends on the type of connection between the RAID array and your Mac.
For external RAID arrays connected via Thunderbolt or USB, you can simply disconnect the RAID from your old Mac, connect it to your new Mac, and access the data. The RAID will be recognized and mounted on the new Mac with minimal steps needed. However, it’s a good idea to recreate the RAID in Disk Utility on the new Mac for redundancy in case of disk failure down the line [1].
For internal RAID arrays, the process involves removing the disks from the old Mac, installing them in the new Mac in the same order, and recreating the RAID in Disk Utility. This retains the data while also making sure the RAID is optimized for the new hardware. You may need to install additional RAID controller cards in the new Mac to match the old setup.
In either case, be sure to have good backups before migrating the RAID, in case any issues arise in the migration process. With proper planning, you can successfully move RAID arrays to new Macs while retaining all data intact.
[1] https://arstechnica.com/civis/threads/transfer-existing-disk-utility-raid-to-new-mac.1485967/
Advantages of Apple RAID
Using Apple’s built-in software RAID offers several key advantages over hardware RAID solutions or third-party software RAID.
In terms of performance, Apple RAID provides improved speed and responsiveness by striping data across multiple drives 1. This allows reads and writes to be distributed across drives for faster access. Additionally, Apple RAID supports disk concatenation, combining multiple drives into one large logical volume.
Apple RAID also offers redundancy and protection against drive failure. Supported RAID levels like RAID 1 provide mirrored copies of data across drives. If one drive fails, data integrity is maintained 2. Rebuilding degraded arrays is handled seamlessly by the operating system.
Finally, Apple RAID provides a simple and seamless user experience. Setup and management is handled through Disk Utility, with no additional software required. Expanding or migrating arrays is straightforward. Apple RAID integrates tightly with macOS for a smooth user experience.
Limitations of Apple RAID
While Apple’s built-in RAID software has some advantages, it also comes with some limitations, especially compared to third-party RAID solutions.
The biggest limitation is that Apple’s RAID implementation is proprietary. It only works with Apple hardware and software. This means RAID arrays created with Apple’s tools can’t easily be migrated to other platforms if you decide to switch away from Mac in the future. There is no standard way to access the data on Apple RAID from non-Apple operating systems Are there usability advantages to macOS’s built-in RAID?.
Apple’s RAID options are also more limited compared to advanced third-party solutions like SoftRAID. For example, Apple only supports RAID 0, 1, and 10, while SoftRAID supports additional RAID 5 and 6 options for parity and fault tolerance Pros & Cons using Apple’s Disk Utility vs SoftRAID. This limits the flexibility to choose the ideal RAID level for your needs.
Monitoring and managing Apple RAID arrays is also less robust. While third-party software offers more advanced features like email alerts, advanced monitoring, and automatic rebuilds, Apple’s tools provide only basic management capabilities Hardware vs Software RAID.
Overall, while Apple’s built-in RAID capabilities work well, they trade flexibility and advanced features for simplicity and tight integration with Apple’s ecosystem.
