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RAID Recovery

Case Study

One recent example of a Kroll Ontrack RAID recovery was with a company called Accius Systems Corporation, whereby their virtual development server, became unresponsive and failed to reboot...


Redundant Array of Independent (originally Inexpensive) Disks (RAID) storage has revolutionised enterprise data storage technology, building in the peace of mind of redundancy (from RAID 1 & above) which can greatly minimise downtime suffered due to individual drive failures. Unfortunately though, RAID storage isn't a perfect technology and as a result data loss can still occur.

Kroll Ontrack, through our Ontrack© Data Recovery services, can provide unmatched proprietary capabilities and resources when a RAID data recovery is required. With almost 30 years' experience and the expertise of a global network of R&D data recovery engineers, nobody gives you a better chance at recovering your business-critical lost data.

RAID Data Storage Levels

As technology evolves the flexibility and capabilities of data storage technology are only going to expand, though coming with it the complexity of the systems themselves. Moore's Law can go a long way to describe this. Already we have seen RAID levels expand from RAID 0 all the way to RAID 51 (and beyond).

Kroll Ontrack has the skills, proprietary tools and experience to recover from all RAID levels, including:

  • RAID 0
  • RAID 1
  • RAID 3
  • RAID 4
  • RAID 5
  • RAID 1E
  • RAID 6
  • RAID 5E
  • RAID 5EE
  • RAID 0+1
  • RAID 10
  • RAID 50
  • RAID 51

Unfortunately data loss risk doesn't limit itself to the RAID controller – the piece of hardware which manages and indexes where each packet of data is stored across each of the drives – individual drives can – and will – fail at some point in their lifetime. When this does happen, if individual drives do fail then, assuming it is a RAID 1 or greater, the faulty drive can just be replaced with a new one and have the data storage map rebuilt with zero data loss. Though if a drive failure exceeds the redundancy capacity of the RAID array, trust Kroll Ontrack to give you the best chance at rebuilding your RAID array and recovering your data.

Modern RAID Arrays

Raid RecoveryGiven the highly complicated and technical nature of modern RAID arrays and how they can be utilised with other highly complicated technologies for significant efficiency and cost benefits, such as virtualisation. It is not uncommon for one of these technologies to suffer a fault, and then combined with other highly complex technologies to potentially cause significant data loss which can cost businesses millions in downtime. It is these types of situations where Kroll Ontrack comes into its own.

Modern RAID arrays can also utilise multiple file systems, like BTRFS or ZFS at hardware level, with NTFS or HFS layered over the top for application support via virtualisation. In the event that one of these file systems have a data loss, Kroll Ontrack can utilise its wealth of experience to assist with your RAID recovery.

Call us today to discuss your RAID data recovery requirements.

How RAID recovery is performed

RAID recovery overview

Redundant Array of Independent Drives , or also known as Redundant Array of Inexpensive Drives (or Disks), and in either respect it is referred to as RAID. RAID is a term used for computer data storage schemes that spread and or replicate data among multiple hard disk drives. RAID was designed with two key goals: to increased data reliability and increased I/O (input/output) performance.

A number of standard configurations were designed which are referred to as levels. There were five RAID levels originally created, but many more variations have evolved, notably several nested levels and many non-standard levels (mostly proprietary).

A RAID combines physical hard disks into a single logical unit by using either special hardware or software. Harsdware RAID solutions can come in a variety styles, from built onto the motherboard or add in cards, up to large enterprise NAS or SAN servers. With these setups the operating system is unaware of the technical workings or the RAID. Software solutions are typically implemented in the operating system.

There are three key concepts in RAID: mirroring, the copying of data to more than one disk; striping, the splitting of data across more than one disk; and error correction, where redundant data is stored to allow problems to be detected and possibly fixed (known as fault tolerance). Different RAID levels use one or more of these techniques, depending on the system requirements.

RAID is traditionally used on servers, but can be also used on workstations. The latter is especially true in storage-intensive computers such as those used for video and audio editing.

Commonly used RAID terms

  • RAID - is a technology that supports the use of 2 or more hard drives in various configurations for the purposes of achieving greater performance, reliability and larger volume sizes through the use of consolidating disk resources and parity calculations.
  • Parity – A mathematical calculation which allows drives within a RAID array to fail without the loss of data. The simplest way to show this is the equation:

A + B = C

You can remove anyone of the letters from above and work out its value from the 2 remaining. I.e. if B was removed so the equation looked like A + ? = C, then B's value can be worked out by moving the A, so B = C – A.

This is obviously a simplistic way of describing it, to fully understand it in a RAID sense, knowledge of binary and the logical XOR expression is required.

Learn more:


  • Mirroring – The data from 1 or more hard drives is duplicated onto another physical disk(s).
  • Striping – The method that data and parity can be written across multiple disks. In the example below the data is written across the drives in an sequential order until the last drive, it then jumps back to the first and starts a 2 nd stripe.

  • Block – A block is the logical space on each disk where the data is written, the amount of space is set by the RAID controller and most commonly would be 16KB to 256KB in size. The data will fill up the space until the limit is reached and then move onto the next drive, until the last drive when it will jump to the start of the next stripe.

  • Left / Right Symmetry – The symmetry in a RAID controls how the data and parity are distributed across the drives. There are 4 main styles of symmetry, which one is used depends on the RAID vender. Some companies also make proprietary styles depending on their business needs.

See RAID 5 for more information on Symmetry.

  • Hot Spare – There are a few different methods for dealing with drive failures within a RAID, one is the use of a Hot Spare. It is a spare disk which can be used in place of the failed one.
  • Degraded Mode – This happens when a drive in the RAID becomes unreadable, the drive is then considered bad and is withdrawn from the RAID. The new data and parity are then written to the remaining drives within the RAID, if any data is requested from the failed drive it is worked out with the parity on the others. This degrades the performance of the RAID, hence degraded mode.

Kroll Ontrack are the global leaders in RAID recovery. If you would like to speak with Kroll Ontrack about your RAID data loss then contact us today.


Partner: Oracle
Kroll Ontrack has a longstanding industry partnership with Oracle.

Partner: HP
Kroll Ontrack have a long historical relationship with HP.

Partner: VMware
Kroll Ontrack can recover data from all VMware virtual environments.

Partner: Microsoft
Kroll Ontrack is a Microsoft Gold Certified Partner.



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RAID Recovery - Kroll Ontrack UK Using proprietary tools & techniques Kroll Ontrack are able to recover mainstream RAID levels & unusual RAID arrays. Contact us today about raid recovery. raid recovery, Data recovery, raid data recovery, raid system recovery, raid 5 recovery