Migrate Logical Drive

For links and interfaces common to all Configuration Wizards links, please see Wizards Overview in ACU help.

The following screens allow you to change the RAID and/or stripe size of a configured logical drive without incurring data loss.

These screens will allow you to change the current level of fault tolerance (RAID type) and/or stripe size for your logical drive. When the fault tolerance and/or stripe size changes, you may have more or less unused space, depending on the fault tolerance and stripe size with which you started.

Your first option will be to select the logical drive(s) you would like to migrate, from those logical drive(s) listed.

The next option will be to select the new fault tolerance for the logical drive.

Fault Tolerance

Note: Some RAID types are only available as options if there is an enabler on the controller allowing that particular RAID choice. Specifically, RAID 4 - Data Guarding and RAID 6 (ADG) - Advanced Data Guarding. If an enabler exists on the controller, the radio buttons for these options will be present as well.

RAID 0 - No Fault Tolerance
This radio button offers the greatest capacity and performance without data protection. RAID 0 provides data striping but no fault tolerance. If you select this option for any of your logical drives, you will experience data loss for that logical drive if one physical drive fails.

However, because no logical drive capacity is used for redundant data, this method offers the best processing speed and capacity. You may consider assigning RAID 0 to drives that require large capacity and high speed, but pose no safety risk.

RAID 1+0 - Drive Mirroring
This radio button offers the best combination of data protection and performance. RAID 1+0 (drive mirroring) creates fault tolerance by storing duplicate sets of data on a pair of disk drives. There must be an even number of drives for RAID 1+0. This is the most costly fault tolerance method because it requires 50 percent of the drive capacity to store the redundant data. RAID 1+0 first mirrors each drive in the array to another, then stripes the data across the mirrored pairs.

If a physical drive fails, the mirror drive provides a backup copy of the files and normal system operations are not interrupted. The mirroring feature requires a minimum of two drives and, in a multiple drive configuration (four or more drives), mirroring can withstand multiple simultaneous drive failures as long as the failed drives are not mirrored to each other.

RAID 5 - Distributed Data Guarding
This radio button offers the best combination of data protection and usable capacity. RAID 5 stores parity data across all the physical drives in the array and allows more simultaneous read operations and higher performance than data guarding (RAID 4). If a drive fails, the controller uses the parity data and the data on the remaining drives to reconstruct data from the failed drive. The system continues operating with a slightly reduced performance until you replace the failed drive.

RAID 5 requires an array with a minimum of 3 physical drives. The capacity of the logical drive used for fault tolerance depends on the number of physical drives in the array. For example, in an array containing 3 physical drives, 33 percent of the total logical drive storage capacity is used for parity data; a 14-drive configuration uses only 7 percent.

RAID 6 (ADG) - Advanced Data Guarding
This radio button will only be available if the controller has an enabler. RAID 6 (ADG) is a fault-tolerance method that provides the highest level of data protection. It is similar to RAID 5 in that parity data is distributed across all drives in the array, except that multiple separate sets of parity data are used in RAID 6 (ADG), and the capacity of multiple drives is used to store the parity data. Simultaneous failure of several drives is thereby tolerated in RAID 6 (ADG), whereas RAID 4 and RAID 5 can only sustain failure of a single drive. The fault-tolerance of RAID 6 (ADG) configurations is actually higher than that of RAID 1+0 configurations, since in RAID 1+0 configurations there is a chance that two drives mirrored to each other will fail simultaneously.

RAID 6 (ADG) read performance is similar to that of RAID 5, since all drives can service read operations, but the write performance is lower than that of RAID 5 because the parity data must be updated on multiple drives. Performance is reduced further in a degraded state.

RAID 6 (ADG) requires an array with a minimum of 2+P physical drives, where P is the number of drives used to store parity data; normally, P= 2. The percentage of the total drive capacity used for fault tolerance is equal to the number of drives used for parity data divided by the total number of physical drives. For example, in an array of five physical drives that has two parity drives, 40 percent of the total logical drive storage capacity is used for fault tolerance. A 14-drive configuration that also has two parity drives uses only 14 percent of storage capacity for fault tolerance.

Note: Some controllers may not support this option. In this case, the Advanced Data Guarding (RAID 6 (ADG)) option will not be available on this screen.

RAID 4 - Data Guarding
This radio button will only be available if the controller has an enabler. RAID 4 is a method that assures data reliability while using only a small percent of the logical drive storage capacity. A designated, single physical drive contains parity data. If a drive fails, the controller uses the data on the parity drive and the data on the remaining drives to reconstruct data from the failed drive. This allows the system to continue operating with slightly reduced performance until you replace the drive.

RAID 4 requires a minimum of 3 physical drives (2 data drives and 1 parity drive) in an array. The capacity of the logical drive used for fault tolerance depends on the number of physical drives in the array. For example, in an array containing 3 physical drives, only 33 percent of the total logical drive storage capacity is used for fault tolerance; while a 14-drive configuration uses only 7 percent.

Some new controllers or firmware versions may no longer support this option. In this case, the Data Guarding (RAID 4) option will not be available.

The next option will be to select the new stripe size for the logical drive from the various options listed.

Stripe Size
The stripe size control is only available if the controller supports stripe size modification. Click on the appropriate radio button to select the stripe size for the logical drive.

The stripe size is useful for fine-tuning the performance of the logical drive. In complicated environments, try various stripe sizes and use the one that performs the best for your situation. Optimizing the stripe size for a particular application may degrade performance of a different application.

Testing with stripe size has produced the following generalities for simple environments:

  • In a mixed read/write environment: The default stripe size is recommended.
  • In an environment with more reads than writes: Larger stripe sizes are typically better.
  • In an environment with more writes than reads: For RAID0, or RAID 1+0, larger stripe sizes are typically better. For RAID4 or RAID5, smaller stripe sizes are typically better.