Which RAID type should I use?

Version 3

    This document is not a summary of storage best practices. Its purpose is to assist in the answering of the question, "What RAID type do I configure my VMFS LUN as?" which is often asked in regards to local storage.

     

    Summary of the different RAID types

    Type

    RAID 0

    RAID 1

    RAID 1+0

    RAID 5

    Method

    Striping

    Mirroring

    Mirror and striping

    Stripe with Parity

    Description

    The data is striped across all the disks in the set. Not true RAID because it is not redundant.

    Exact copies of the data are kept across paired disks or disk sets.

    A striped array whose segments are a mirror set. Not to be confused with 0+1

    The data is striped across all the disks in the RAID set, along with the parity information needed to reconstruct the data in case of disk failure.

    Performance

    Good. All IO is spread and no parity overhead

    Twice the read rate but writes occur twice

    Combines speed efficiency of the RAID 0 (stripe set) with a fault tolerance of RAID 1 (mirror).

    High read and medium write performance. A good balance of performance and availability.

    Typical use

    Data you can afford to loose, such a pre-production, image/video editing.

    Data requiring high availability, such as accounting or payroll.

    Transactional type data such as database logs.

    File and application servers. Typically everything that does not have a specific requirement.

    Parity Calculation

    None

    None

    None

    Yes

    Redundancy

    None

    Yes

    Yes

    Yes

    Minimum Disks

    2

    2

    4

    3

    Storage Overhead

    0%

    100%

    100%

    Capacity of one disk in the set. 33% for a 3 disk set.

     

    Other elements to consider are

    • Hot spare disks can often be configured to provide a space to rebuild a redundant disk without attendance.

    • Some types of SAN behave differently under the hood and you should reference the vendor documentation and best practices. For example the HP EVA works quite differently and some vendors have RAID 6.

    • For optimal performance make sure VMFS is the only partition on LUN and make sure the LUN maps to it's own set of physical disks if possible.

     

    Further reading

     

    Document maintenance

    This document is open for public maintenance in order to be a living document maintained by the community. Please update as required with the following guidelines.

     

    • Attempt to keep formatting consistent and simple.

    • Mark revisions as required. Minor edits don't need to be new versions.

    • Post a comment describing changes to the document rather than inserting revision information into the document in order to keep the document uncluttered.

    • Try to stick to the facts rather than opinions.

    • References to further reading are helpful.