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Disk Utility 12.x: Create a RAID set

Create a RAID set using Disk Utility

If you have one or more internal or connected external disks, you can create a Redundant Array of Independent Disks (RAID) set to optimize performance and increase reliability in case of a disk failure. The type of RAID set you choose depends on whether you want to protect your data, speed up access to your data, or increase your storage capacity.

RAID disk sets and Concatenated disk sets will not be able to use some disk management features such as FileVault disk encryption.

If you have a Mac Pro with a Mac Pro RAID card, use RAID Utility (in the Utilities folder in Launchpad). It uses the RAID card for better performance and to create more types of RAID sets.

Create a mirrored RAID set

Protect your data against hardware failure with a mirrored RAID set (also called “RAID 1”). It writes your data to two or more disks so that each disk in the set contains the same data as every other disk.

You can’t create a RAID set that contains partitions on your startup disk. To create a RAID disk that contains partitions on that disk, you must first start up your computer from another disk or the Mac OS X installation disc.

  1. Open Disk Utility, in the Utilities folder in Launchpad.
  2. Select one of the disks that you want in the set, and then click RAID.
  3. Click Add (+), and type a name for the RAID set.
  4. Choose a format from the Format pop-up menu, and then choose Mirrored RAID Set from the RAID Type pop-up menu.
  5. Drag the disks you want to add to the set to the list on the right.
  6. For each disk, select it, and then choose its type from the RAID Type pop-up menu.
    • To use the disk as a mirror at all times, choose RAID Slice.

    • To use the disk as a mirror only when another disk fails, choose Spare. A disk can be a spare in only one RAID set.

      If a disk in the set fails and you have no spares, you must add a new disk to the RAID set in Disk Utility to return to the original number of disks.

  7. To rebuild disks automatically when they’re disconnected then reconnected, click the Options button, select RAID Mirror AutoRebuild, and click OK.

    If you don’t choose to rebuild disks automatically, you must rebuild them yourself in Disk Utility.

  8. Click Create.

Create a striped RAID set

Speed up access to your data with a striped RAID set (also called “RAID 0”).

You can’t create a RAID set that contains partitions on your startup disk. To create a RAID disk that contains partitions from that disk, you must first start up your computer from another disk or the Mac OS X installation disc.

  1. Open Disk Utility, in the Utilities folder in Launchpad.
  2. Select one of the disks that you want in the set, and then click RAID.
  3. Click Add (+), and type a name for the RAID set.
  4. Choose a format from the Format pop-up menu, and then choose Striped RAID Set from the RAID Type pop-up menu.
  5. Drag the disks you want to add to the set to the list on the right.
  6. Click the Options button to specify an optimal storage block size for the data stored on the set.

    Set the block size to match the size of data stored on the set. For example, a database might store small units of data, so a small block size might be best. A video processing application might require fast throughput of large amounts of data, so a larger block size might be best.

  7. Click Create.

Create a concatenated disk set

Increase storage space with a concatenated RAID set (also called “Just a Bunch of Disks” or JBOD). If you need one large disk, but you have only several smaller disks, you can create a concatenated disk set to use several small disks as one large disk.

  1. Open Disk Utility, in the Utilities folder in Launchpad.
  2. Select one of the disks that you want in the set, and then click RAID.
  3. Click Add (+), and type a name for the RAID set.
  4. Choose a format from the Format pop-up menu. Usually you’ll choose the Mac OS Extended (Journaled) format.
  5. Choose Concatenated Disk Set from the RAID Type pop-up menu.
  6. Drag the disks you want to add to the set to the list on the right.
  7. Click Create.

Combine RAID sets

Combine different RAID sets to combine their benefits. For example, if you have two 40 GB FireWire disks and an 80 GB internal disk, you can create a concatenated disk set with the two FireWire disks, and then create a mirrored RAID set with the concatenated set and the internal disk. Or, if you have four disks with fast connections, you can create a set that combines the fast disk access of a striped RAID set and the data protection of a mirrored RAID set, also called “RAID 10.”

First, set up the smaller RAID sets that will be in the larger RAID set. Then, when creating the larger RAID set, drag the smaller RAID sets to it as its disks. (Drag the partition icons that are under and slightly to the right of the RAID set’s icon in the list at the left.)

Last Modified: Jul 11, 2012
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  • Last Modified: Jul 11, 2012
  • Article: PH5834
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