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RAID levels supported by HP array controllers

HP array controllers support the following RAID levels:

  • RAID 0 - Disk striping

  • RAID 1+0

  • RAID 5

  • RAID ADG

    Selecting the appropriate RAID level

    The following table provides suggested RAID levels based on the customer requirements:

    Most important Also important Suggested RAID level
    Fault tolerance Cost effectiveness RAID ADG
    I/O performance RAID 1 + 0
    Cost effectiveness Fault tolerance RAID ADG
    I/O performance RAID 5 (RAID 0 if fault tolerance is not required)
    I/O performance Cost effectiveness RAID 5 (RAID 0 if fault tolerance is not required
    Fault tolerance RAID 1 + 0
  •  

    RAID 0 - Disk striping

    RAID 0 distributes volume segments across multiple disk drives and speeds up operations that retrieve data from disk storage. It is the least costly. RAID 0 characteristics include:

    • Not fault-tolerant

    • No redundancy

    • Data is striped across all drives

    • Requires two drives for a striped set (although Smart Array controllers can create a logical drive from one drive, but with no redundancy)

    • 100% available disk space

    • Excellent read and write performance

    • All data is lost if one of the drives fails

     

    RAID 1+0

    The most expensive of RAID configurations, RAID 1+0 combines RAID 1 mirroring with RAID 0 striping. The drives are first mirrored and then striped across the member disks. RAID 1+0 has good performance and redundancy, but also has write penalties (two physical write requests for one logical write request).

    This array configuration can withstand the loss of several disks as long as they do not belong to the same mirrored pair. If two disks in the same mirrored pair fail, the data is lost. This means that RAID 1+0 cannot guarantee protection against a two-disk failure.

    In a RAID 1+0 configuration, all HP Smart Array controllers can:

    • Sustain an entire bus failure if the drives are equally distributed across the buses

    • Service I/O requests to all operational drives in a degraded condition

    • Survive n/2 drive failures, where n is the number of drives in the array, as long as one member of each mirrored pair survives

     

    RAID 5
     

    RAID 5 provides data striping and stripe error correction information. For RAID 5, HP recommends that no more than 14 (8 is optimal) physical drives be used per logical drive with HP Smart Array controllers. A minimum of three drives is required. One drive can fail without a service interruption. Concurrent access and distributed parity are properties of RAID 5.

     

    RAID ADG

    Only select Smart Array controllers offer HP Advanced Data Guarding (RAID ADG), which offers:

    • Higher fault tolerance than RAID 5

    • Lower implementation costs than RAID 1+0

    • Greater usable capacity per U than RAID 1

    When using the HP patented RAID ADG technology, you can safely deploy large-capacity hard drives and create large storage volumes. RAID ADG is a proprietary version of RAID 6 and it is thus frequently called RAID 6.

    RAID ADG protects data from multiple drive failures and is able to withstand two simultaneous hard drive failures without data loss or downtime.

    RAID ADG uses two sets of parity striped across the disks. This method provides protection for an array with up to 56 drives and requires only two drives to store the parity information. To implement RAID ADG, a minimum of four drives is required.

    Although RAID ADG provides the dual advantages of increased fault tolerance and high capacity, it does so at the cost of performance, which is less than that of other RAID levels. The RAID ADG performance equals RAID 5 performance when reading data, but it is slower when writing data because of the extra parity data.