It's a good idea to erase and format all the disks that were part of the deleted array. In this section, we're going to look at creating and managing a RAID 1 array , also known as a mirrored array. Mirrored arrays replicate data across two or more disks, with the main goal of increasing reliability by creating data redundancy , assuring that if a disk in a mirrored array were to fail, data availability would continue without interruption. Adding more disks to the array increases overall reliability by the power of the number of disks in the array.
You can learn more about RAID 1 requirements and how to calculate reliability by reading the guide: RAID 1: Mirroring Hard Drives. With the requirements out of the way, let's get started creating and managing your mirrored RAID array. Make sure the disks that will make up your mirrored array are attached to your Mac and mounted on the desktop. There may come a time when you wish to add slices to the mirrored RAID array. You may want to do this to increase reliability, or to replace older slices that may be showing issues.
You may want to remove a slice to replace it with another, newer disk, or as part of a backup or archiving system. Disks that are removed from a RAID 1 mirror will usually have the data preserved. This allows you to archive the data in another safe location without disturbing the RAID array. The "usually" disclaimer applies because in order for the data to be retained, the file system on the removed slice needs to be resizable. If the resizing fails, all data on the removed slice will be lost.
But Repair has an entirely different meaning here. Once the "repair" process is complete, you should remove the RAID slice that failed and prompted you to run the Repair process. You can completely remove a mirrored array, returning each slice that makes up the array back to general use by your Mac.
By striping a pair of mirrored arrays, you increase reliability while maintaining the improved performance available in a striped array. RAID 10 requires at least four disks , broken into two striped sets of two disks. Best practices say the disks should be from the same manufacturer and be of the same size, although technically, it's not an actual requirement.
I do, however, recommend you adhere to best practices. Nevertheless, it's a useful method of using multiple disks to create a single larger volume for storage. The requirements for creating a JBOD array are quite loose. Disks that make up the array can be from multiple manufacturers, and disk performance doesn't need to be matched.
JBOD arrays provide neither a performance increase nor any kind of reliability increase. Although it may be possible to recover data using data recovery tools, it's likely a single disk failure will lead to lost data. As with all RAID arrays, having a backup plan is a good idea. Before you begin, make sure the disks you wish to use for the JBOD array are attached to your Mac and mounted on the desktop.
If you find yourself running out of space on your JBOD array, you can increase its size by adding disks to the array.
Replace a failed disk in a Disk Utility RAID 1 - Ask Different
Make sure the disks you wish to add to the existing JBOD array are attached to your Mac and mounted on the desktop. It's possible to remove a disk from a JBOD array, although it's fraught with issues. The disk being removed must be the first disk in the array, and there must be enough free space on the remaining disks to move the data from the disk you're planning to remove to the disks that remain in the array. Resizing the array in this manner also requires that the partition map be recreated.
Any failure in any part of the process will cause the process to be aborted and the data in the array to be lost. Share Pin Email. Tom Nelson has written hundreds of articles, tutorials, and reviews for Other World Computing and About. He is the president of Coyote Moon, Inc.
RAID 1 - Slice failed - How to rebuild
Updated October 15, If you need assistance with creating a backup, check out the guide: If you're ready, let's get started. The method to calculate the failure rate of a striped array, assuming all disks in the array are the same, is: Only those disks that meet the requirements for the selected RAID type will be highlighted, allowing you to select them. The usual requirements are that they must be formatted as Mac OS Extended Journaled , and can't be the current startup drive.
Select at least two disks. This should be the accepted answer as it uses the Disk Utility as of the original question, while the command line approach of course also is helpful. Sherwood Botsford Sherwood Botsford 1, 1 11 Sign up or log in Sign up using Google.
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Disk Utility is also a disk repair tool. Using the First Aid option, you can address problems with your hard drive and potentially repair a damaged or corrupted disk. First, you have to start the utility. Upon opening Disk Utility you are presented with a view of the drives that are currently attached to your system. Internal and external drives are listed separately. The View drop-down in the top left corner lets you view all devices or just the logical volumes. Select a volume or device by clicking on it to obtain information about your selection.
macOS Disk Utility Can Create Four Popular RAID Arrays
You will see the currently used and free space on the disk as well as its capacity, mount point, type of drive, and the file system used on the disk. The options are:. A volume option is also on the top of the menu and allows you to add or delete volumes to a container if available for your selection. Care needs to be taken when formatting disks. An inadvertent format of the wrong disk can cause some serious problems and data loss, so proceed with caution.
One of the main uses of Disk Utility is to repair a disk. You will want to perform this task if your hard drive is experiencing problems such as slow access time or missing and corrupted files. Follow this procedure to repair a disk. Hopefully, after running First Aid, your disk problems will be resolved. If not, you may need to engage in further investigation. Disks that appear in the listing of available devices are normally already mounted.
You will be able to Mount or Unmount the disk based on its current state. These options are on the top menu and are only highlighted when the command can be used on your selected disk. Disk Utility can also be used to restore a disk from another connected disk.
The restore function destroys all data on the destination disk so should be used with caution. While Disk Utility is a great tool that allows you to better understand your disks and perform many important tasks on them, it does have certain limitations. You may find that running First Aid is not enough to repair your disk and make it fully operational again.