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What is RAID and what are the different RAID modes?

Note: Not all StarTech.com devices support each of the RAID modes described below. For more information on the RAID modes that your device supports, refer to the manual or the StarTech.com product page.

Redundant Array of Independent Disks (RAID) is a virtual disk technology that combines multiple physical drives into one unit. RAID can create redundancy, improve performance, or do both.

RAID should not be considered a replacement for backing up your data. If critical data is going onto a RAID array, it should be backed up to another physical drive or logical set of drives.

The following are terms that are normally used in connection with RAID:

  • Striping: data is split between multiple disks.
  • Mirroring: data is mirrored between multiple disks.
  • Parity: also referred to as a checksum. Parity is a calculated value used to mathematically rebuild data.

Different RAID levels exist for different application requirements.

Refer to the following table for the list of RAID modes offered by some StarTech.com products:

RAID mode Description Operation Advantages Disadvantages Recovery
RAID 0 Striped disks Data is split evenly between two or more disks. Large size and the fastest speed. No redundancy. If one or more drives fails, this results in array failure.
RAID 1 Mirrored disks Two or more drives have identical data on them. A single drive failure will not result in data loss. Speed and size is limited by the slowest and smallest disk. Only one drive is needed for recovery.
RAID 3 Striped set with dedicated parity Data is split evenly between two or more disks, plus a dedicated drive for parity storage. High speeds for sequential read/write operations. Poor performance for multiple simultaneous instructions. A single drive failure will rebuild.
RAID 5 Striped disks with distributed parity Data is split evenly between three or more disks. Parity is split between disks. Large size, fast speed, and redundancy. The total array size is reduced by parity. A single drive failure will rebuild.
RAID 10 1+0; Striped set of Mirrored Subset Four or more drives are made into two mirrors that are striped. Larger size and higher speed than RAID-1, and more redundancy than RAID-0. No parity. Only one drive in a mirrored set can fail.
JBOD Just a Bunch Of Disks Any number of drives are accessed independently by the operating system. Software RAID modes can be used. Hardware RAID may have better performance. N/A
Big Spanning or Concatenation Data is written on one drive until it is full, and then the next drive(s) until it or they are full. Creates a very large and simple array.

No redundancy.

N/A
Clone RAID 1 + Spare

Two drives have identical data, plus one drive is used for rebuilding in case of a primary array failure.

Seamless operation when one drive fails in a RAID-1 array. Spare drive is not accessible to the user. Only one drive is needed for recovery.