Ontrack Data Recovery

Data Recovery Resources > Supported RAID levels

Supported RAID levels

 

Kroll Ontrack offers Raid recovery services for all the mainstream Raid levels; this covers but is not limited to Raid Levels 0, 00, 1, 10, 1E, 1E0, 2, 3, 4, 5, 50, 5E, 5EE, 6 and 60.

We also support a lot of proprietary Raid array systems. The ongoing development of our software tools insures we utilise the very latest techniques to produce the best recoveries possible; our development team can also used to create bespoke tools for proprietary and unusual Raid arrays.

We have support for a lot of the vendor specific Raids from companies suc as HP, Compaq, Dell, Adaptec, IBM, Intel, Promise, LSI Logic, Mylex, Xiotech and Netsan. All of these have there own Raid configurations, Data block sizes, Parity sizes and symmetry.

Our Raid recovery capabilities don’t just stop at NTFS Based Raids; we also have extensive capabilities with MAC, UNIX, FAT and VMware Raids. With over 250 Engineers worldwide, our knowledge base is second to none.

Raid 0

Raid 0 is the classic data stripping configuration, data is written across all the drives resulting in much higher data throughout. This higher performance comes at a cost, if one or more drives fail within a Raid 0 severe data loss can occur.

The diagram below shows how the data walks across the array.

An Example of a Data recovery situation; a file was created that occupied data stripes 1 – 4, if drive 2 were to fail and the 2 nd stripe lost the file would most likely become corrupted. Another way to look at it would be if one drive fails, the largest possible good file would have to be smaller than the combined size of the remaining stripes.

Raid 1

This is the basic data mirroring Raid level, data from the primary drive is duplicated on to the other. There are no performance gains from this raid level but if one drive fails you will have a backup on the 2 nd.

Raids 0+1 and 1+0

To gain performance and/or additional redundancy the standard Raid levels can be combined to create hybrid or Nested Raid levels, Raid types that provide redundancy are typically combined with RAID 0 to boost performance.

As you can see from the diagrams below these 2 raid levels are a combination or Raid 0 and Raid 1. The difference between the 2 is the location of the actual Raid array, this is show on the diagrams where the stripes are in bold.

Raid 01 is configured so the Raid 0 has a mirror copy.

The advantage is that when a drive fails in one of the level 0 arrays, the missing data can be transferred from the other array. However, adding an extra hard drive to one stripe requires you to add an additional hard drive to the other stripes to balance out storage among the arrays.

A disadvantage for this configuration is that is cannot recover from 2 simultaneous drive failures, unless the drives are from the same data stripe. In the diagram below; if drives 1 and 5 failed the raid could be rebuild but if 1 and 4 failed it would result in data loss.

Raid 10 is configured so that the Raid 0 is split across two Raid 1 arrays.

A big advantage to Raid10 is all but one drive from each RAID 1 array could fail without any data loss. However, if the failed drive is not replaced, the single working drive in that array becomes a single point of failure for the entire system, if that last drive goes all data within the array is lost.

The Raid nesting technique can be used for other Raid levels as well, most commonly on Raid 5 but it can also be applied to other levels like 3 and 6, producing levels such as 50, 51, 60, 61, 30 and 03.

Raid 2

Raid 2 comprises of data striping at a bit level with a dedicated parity drive. This level uses hamming error detection codes and is intended for use on drives that do not have built-in error detection. For this reason Raid 2 is not commonly used anymore.

Raid 3 & 4

Raids 3 and 4 both use striping with a dedicated parity drive, the difference between the two is that Raid 3 stripes at the byte level while Raid 4 stripes at the block level.

Raid 3 is seldom used these days due to the poor performance of byte level striping, Raid 4 is better with block level striping but still suffers slower write performance due to the parity having to be updated on every write.

Raid 5

Raid 5 is generally considered to be the best compromise between fault-tolerance, speed and cost. It stripes the data in the same way as a Raid 0, but it also stripes the parity information across all the drives as well. How the Raid array distributes the parity and data across the drives is vender specific but will almost always be 1 of 4 ways, left asymmetric, left symmetric, right asymmetric and right symmetric. In the diagrams below you can see how the data moves over or round the parity, also the direction of the parity across the drives.

The direction of the parity is the easiest to spot, as you can see it either slopes to the right or left. Within Asymmetric Raids the data stripes ignore the parity, jumping over it to the next available space. Symmetric Raids are a little more complex with the data striping, once the data hits a parity block it will move across and down onto the next stripe set.

Raid 6

Raid 6 is an extension of Raid 5; it follows the same Data and parity distribution but with an added parity block in each stripe. The main reasoning behind this is you can have 2 simultaneous drive failures and the raid will not lose any data. In smaller Raids the chance of 2 drives failing within a short period of time is slim, but as Raid arrays grow in size so does the probability of drive failures. For this reason Raid 6 is normally only recommended in larger Raid systems.

Performance wise it is very similar to Raid 5, write speeds are high because the data and parity can be written to all the drives but read access is slower due to the delay is skipping 2 sets of parity.

RAID Data Recovery Service Options

  • Remote Recovery Services – If the problem with your raid is logical then there is no reason why we cannot perform the recovery remotely. This could cover data loss situations like a simple file deletion, lost partitions, formats and even complete loss of Raid configuration. All these can be done with the drives never even leaving your premises. This is by far the fastest option to getting your data back, without the need or cost of shipping the drives to us.
  • In-Lab Data Recovery Services – Our in house lab has the most extensive Data Recovery capabilities possible, with our own cleanroom on-site to get your physically damaged drives working again. All the logical failures that can be done remotely can also be done at our lab. The drives you send to our lab will be returned in exactly the same state as you sent them, your recovered data will be sent back to you on either External USB / FireWire drive.
  • On-Site Data Recovery Services - In cases where moving storage media would require too much downtime or your business security is very high - performing data recovery procedures right at your facility may be the best option. Our security cleared engineers can be sent to your office to perform the recovery right there or alternatively if a large number or drives are involved; we can image the drives and take the images back to our lab to work on, minimizing your users downtime.
  • Development for Proprietary Systems - Our world wide team of developers are always ready to create bespoke software tools to handle any proprietary system. Databases, Raids and even old or generally unsupported file systems can be looked into.